0000755001-26-000023 | 11-K | XBRL Viewer

NEW YORK LIFE STABLE VALUE FUND	12 Months Ended
Dec. 31, 2025
EBP 002 [Member]
Employee Benefit Plan Stable Value Fund [Line Items]
NEW YORK LIFE STABLE VALUE FUND	NOTE F - NEW YORK LIFE Stable Value Fund The investment in the Stable Value Fund is a contractual account with New York Life Trust Company (“New York Life”). New York Life maintains the Plan’s contributions in a separate account. The account is credited with earnings on the underlying investments and charged for participant withdrawals and administrative expenses. The investment contract issuer, New York Life, is contractually obligated to repay the principal and a specified interest rate that is guaranteed to the Plan. The crediting rate is based on a formula established by the contract issuer but may not be less than zero percent. Such interest rates are reviewed on a quarterly basis for resetting. The contract does not have a maturity date. The Plan must provide 12 months’ notice to the contract issuer to redeem its interest in this investment at contract value. Contract value is the relevant measurement attribute for the portion of net assets available for benefits attributable to the investment contract because the investment contract is fully benefit-responsive. The Statements of Net Assets Available for Benefits presents the New York Life Stable Value Fund at contract value. Participants may ordinarily direct the withdrawal or transfer of all or a portion of their investments at contract value. Certain events could limit the ability of the Plan to transact at contract value with the issuer. Such events include the following: (1) total or partial Plan termination; (2) changes to the Plan’s prohibition on competing investment options; (3) mergers; (4) spin-offs; (5) lay-offs; (6) early retirement incentive programs; (7) sales or closings of all or part of a participating plan sponsor’s operations; (8) bankruptcy; (9) receivership; or (10) the failure of the trust to qualify for exemption from federal income taxes or any required prohibited transaction exemption under ERISA. The Plan administrator does not believe that the occurrence of any such event, which would limit the Plan’s ability to transact at contract value with participants, is probable.

TAX STATUS	12 Months Ended
Dec. 31, 2025
EBP 002 [Member]
EBP, Tax Status [Line Items]
TAX STATUS	NOTE E - TAX STATUS The Internal Revenue Service (“IRS”) has determined and informed the Company by a letter dated September 1, 2022, that the Plan, including amendments made through November 8, 2021, and related trust are designed in accordance with applicable sections of the Code. The Plan administrator believes that the Plan is designed, and is currently being operated, in compliance with the applicable requirements of the Code and, therefore, believes that the Plan is qualified, and the related trust is tax-exempt.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies) - EBP 002 [Member]	12 Months Ended
Dec. 31, 2025
EBP, Accounting Policy [Line Items]
Basis of Accounting	Basis of Accounting The financial statements of the Plan are prepared under the accrual basis in accordance with accounting principles generally accepted in the United States of America (“US GAAP”).
Management Estimates	Management Estimates The preparation of the financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and changes therein, and disclosure of contingent assets and liabilities. Accordingly, actual results may differ from those estimates.
Investment Valuation and Income Recognition	Investment Valuation and Income Recognition Registered investment companies (mutual funds) and money market funds are valued at quoted market prices, which represent the net asset value of shares held by the Plan at year-end. Investments in the New York Life Stable Value Fund are valued at contract value, based on information provided by the trustee. (See Note F). The Unitil Corporation Stock Fund is stated at fair value as determined by quoted market prices of both Unitil common stock and cash equivalents held in the fund. Interest income is recorded when earned. Dividends are recorded on the ex-dividend date. The Plan presents in the Statement of Changes in Net Assets Available for Benefits the net appreciation (depreciation) in the fair value of investments, which consists of the realized gains or losses and the unrealized appreciation (depreciation) on those investments.
Notes Receivable from Participants	Notes Receivable from Participants Notes receivable from participants are measured at their unpaid principal balance plus any accrued but unpaid interest. Delinquent notes receivable from participants are recorded as distributions based on the terms of the Plan document.
Payment of Benefits	Payment of Benefits Benefit payments to participants are recorded when paid.
Expenses	Expenses Non-standard service expenses are paid by the Company as provided in the Administration Agreement between the Company and John Hancock Retirement Plan Services LLC (“JHRPS”). Recordkeeping and third-party advisory expenses are paid through an asset charge that is deducted pro rata across all participants on a quarterly basis. A portion of the asset charge is deposited into the Plan Expense Reimbursement Account ("PERA") to pay for third-party advisory fees. At year-end, if there is an excess amount in the PERA, JHRPS is directed by Unitil to reallocate the excess back to participant accounts on a pro rata basis. If, however, the deduction to the PERA account does not cover the third-party advisory fees and other plan expenses the plan is invoiced directly. The fund expense ratios reflected on the 404(a)(5) Participant Fee disclosure are used to cover the fund management fees only; all other plan expenses are covered through the participant asset charge as previously stated.

FAIR VALUE OF PLAN ASSETS

12 Months Ended

Dec. 31, 2025

EBP, Investment, Fair Value and NAV [Line Items]

NOTE G - FAIR VALUE OF PLAN ASSETS

The Plan follows the guidance set forth by the Financial Accounting Standards Board (“FASB”) for reporting fair value of Plan investments. The FASB guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows:



Level 1 -	Inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date.

Level 2 -	Valuations based on quoted prices in markets that are not active or for which all significant inputs are observable, either directly or indirectly.

Level 3 -	Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable.

To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

Fair value is a market-based measure considered from the perspective of a market participant rather than an entity-specific measure. Therefore, even when market assumptions are not readily available, the Company’s own assumptions are set to reflect those that market participants would use in pricing the asset or liability at the measurement date. The Company uses prices and inputs that are current as of the measurement date, including during periods of market dislocation. In periods of market dislocation, the observability of prices and inputs may be reduced for many instruments. This condition could cause an instrument to be reclassified from Level 1 to Level 2 or from Level 2 to Level 3.

Valuation Techniques

There have been no changes in the valuation techniques used during the current period.

Registered Investment Companies

These securities, consisting of mutual funds, are valued based on quoted prices from the market. These securities are categorized in Level 1 as they are actively traded and no valuation adjustments have been applied.

Unitil Corporation Stock Fund and PIMCO Money Market Fund

This fund includes publicly traded common stock of Unitil Corporation valued at quoted prices available on the New York Stock Exchange (categorized as Level 1) as well as cash and cash equivalents held in the PIMCO Money Market Fund. The PIMCO Money Market Fund is categorized as Level 1 as it is actively traded and no valuation adjustments have been applied.

Assets measured at fair value on a recurring basis as of December 31, 2025 and 2024 are as follows:


	Fair Value Measurements at Reporting Date Using
Description	Balance as of December 31,		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
2025
Registered Investment Companies	$	153,994,534	$	153,994,534	$	—	$	—
Common Stock Fund		11,552,966		11,552,966		—		—
Total Investments at Fair Value	$	165,547,500	$	165,547,500	$	—	$	—

2024
Registered Investment Companies	$	132,071,752	$	132,071,752	$	—	$	—
Common Stock Fund		12,120,800		12,120,800		—		—
Total Investments at Fair Value	$	144,192,552	$	144,192,552	$	—	$	—

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

- Definition

The entire disclosure for fair value of investment held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), including, but not limited to, fair value measured at net asset value per share as practical expedient (NAV).

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+ Details

TAX STATUS (Additional Information) (Details) - EBP 002 [Member]	12 Months Ended
Dec. 31, 2025
EBP, Tax Status [Line Items]
Determination Date	Sep. 01, 2022
EBP, tax determination letter, obtained	true

DESCRIPTION OF PLAN (Additional Information) (Details) - EBP 002 [Member]	12 Months Ended
	Dec. 31, 2025 USD ($) Loans Portfolio	Dec. 31, 2024
EBP, Description of Plan [Line Items]
Employee benefit plan, participant maximum contribution percentage	85.00%
Employee benefit plan, participant minimum contribution percentage	1.00%
Employee benefit plan, participant annual contribution increase percentage	1.00%
Employee benefit plan, percentage of employee compensation matched	3.00%
Employee benefit plan, participant automatic contribution rate	6.00%
Employee benefit plan, participants minimum borrowing amount	$ 1,000
Employee benefit plan, participants maximum borrowing amount	$ 50,000
Employee benefit plan, participants maximum borrowing percentage of vested balance	50.00%
Employee benefit plan, loan rate in addition to prime rate	1.00%
Employee benefit plan, maximum number of loans \| Loans	2
Employee benefit plan, number of loans \| Loans	244
Employee benefit plan investment portfolio \| Portfolio	35
Employee benefit plan, stock fund cash and cash equivalent percentage	3.00%	4.00%
Employee benefit plan, stock fund common stock percentage	97.00%	96.00%
EBP In-Kind Distributions	$ 15,790
Maximum [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan, participant maximum contribution percentage	85.00%
Employee benefit plan, participants loan terms	5 years
Employee benefit plan loan maturity date	2039
Employee Benefit Plan, Percentage of Participant Loans	9.50%
Minimum [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan, participants loan terms	1 year
Employee benefit plan loan maturity date	2026
Employee Benefit Plan, Percentage of Participant Loans	4.25%
United Steel Workers [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan, company contribution percentage	4.00%
United Steel Workers [Member] \| Maximum [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan, percentage of employee compensation matched	6.00%
Primary Residence [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan, participants loan terms	15 years
Utility Workers Union of America [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan, company contribution percentage	4.00%
Utility Workers Union of America [Member] \| Maximum [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan, percentage of employee compensation matched	6.00%
International Brotherhood of Electrical Workers [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan, company contribution percentage	4.00%
International Brotherhood of Electrical Workers [Member] \| Maximum [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan, percentage of employee compensation matched	6.00%
UWUA [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan, company contribution percentage	4.00%
UWUA [Member] \| Maximum [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan, percentage of employee compensation matched	6.00%
LIUNA [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan, company contribution percentage	4.00%
Employee contribution matching percentage	100.00%
LIUNA [Member] \| Maximum [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan, percentage of employee compensation matched	6.00%
Non Union Employees [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan, company contribution percentage	4.00%
Employee contribution matching percentage	100.00%
Non Union Employees [Member] \| Maximum [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan, percentage of employee compensation matched	6.00%

EMPLOYEE BENEFIT PLAN, STATEMENTS OF NET ASSETS AVAILABLE FOR BENEFITS - EBP 002 [Member] - USD ($)	Dec. 31, 2025	Dec. 31, 2024
EBP, Statement of Net Asset Available for Benefit [Line Items]
Investments at Fair Value	$ 165,547,500	$ 144,192,552
Investments at Contract Value	9,815,758	9,775,375
Notes Receivable from Participants	2,354,207	2,264,125
Net Assets Available for Benefits	$ 177,717,465	$ 156,232,052

- Definition

Fair value of investment, excluding plan interest in master trust, held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Includes, but is not limited to, derivative, investment measured at net asset value per share as practical expedient, and insurance contract not meeting fully-benefit responsive investment criteria.

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+ Details

DESCRIPTION OF PLAN	12 Months Ended
DESCRIPTION OF PLAN	Dec. 31, 2025
EBP 002 [Member]
EBP, Description of Plan [Line Items]
DESCRIPTION OF PLAN	NOTE A - DESCRIPTION OF PLAN The following description of the Unitil Corporation (“Unitil” or the “Company”) Tax Deferred Savings and Investment Plan (“Plan” or “401(k) Plan”) provides only general information. Participants should refer to the Plan Document for a more complete description of the Plan’s provisions. General The Plan is a defined contribution plan covering all employees of the Company and its wholly-owned subsidiaries Unitil Service Corp., Unitil Energy Systems, Inc., Fitchburg Gas and Electric Light Company, Northern Utilities, Inc., Bangor Natural Gas Company, Maine Natural Gas Corporation and Granite State Gas Transmission, Inc. (collectively, the “subsidiaries”), who satisfy the eligibility requirements. The Company has engaged John Hancock Trust Company LLC (“John Hancock” or “Trustee”) as the trustee of the Plan. The Plan is subject to the provisions of the Employee Retirement Income Security Act of 1974 (“ERISA”) and the Internal Revenue Code (the “Code”). The Plan’s effective date is July 1, 1985. The Plan was amended and restated effective January 1, 2021 to comply with current federal regulations and to incorporate all previous amendments. Eligibility Employees are eligible to participate in the Plan on the first of the month following: (1) Attainment of age 18, and (2) Completion of 1,000 hours of credited service for employees hired before 09/01/2024, as defined by the Plan Document. Participant Contributions Participants may contribute from 1% to 85% of their compensation, as defined by the Plan Document or as limited by the Code, on a pre-tax and/or after-tax basis. Participants may elect to apply the deferral percentage to either (1) base pay, as defined by the Plan Document, or (2) total pay including bonuses, commissions, incentive, overtime and all other forms of premium pay. Participants who are age 50 or will turn age 50 by the end of the Plan year (December 31) may be eligible to make “catch-up” contributions, as defined by the Plan Document and the Code. Participants may also make rollover contributions into the Plan from other qualified plans. New employees are automatically enrolled in the 401(k) Plan, with the automatic employee contribution rate of 6%. This contribution rate will automatically increase by 1% on January 1st of each year until the employee’s contribution is 85% of pay. Employees may elect to opt-out of the automatic enrollment and/or automatic increase features provided by the enhanced Plan benefits. The Plan has a Roth 401(k) option for participants. Contributions made by participants under the Roth 401(k) option are on an after-tax basis. Combined Roth 401(k) and pre-tax deferrals are subject to Code limits. In-plan Roth Rollovers and Roth Conversions will be allowed effective with the addition of the Roth 401(k) option. Employer Contributions The Company matches participant contributions on a dollar-for-dollar basis, up to the first 3% percent of their eligible compensation, as defined by the Plan Document, except as noted below. Overtime pay, commissions and other forms of premium pay are not included in the definition of compensation eligible for matching purposes. For non-union employees who are hired on or after January 1, 2010, and for non-union employees who elected to move from the Company’s existing Pension Plan and accept a frozen pension benefit, the Plan provides enhanced Plan benefits including the Company contributing 4% of eligible compensation, as defined by the Plan, each year, regardless of whether or not the non-union employee elects to contribute to the 401(k) Plan. The Company also matches 100% of these employees’ elective deferrals up to 6% of compensation. For those United Steel Workers (“USW”) Local 12012-6 members who are hired on or after January 1, 2011, and for USW Local 12012-6 members who elected to move from the Company’s existing Pension Plan and accept a frozen pension benefit, the Plan provides for enhanced Plan benefits including the Company matching employee elective deferrals up to 6% of base pay and the Company contributing 4% of base pay each year, regardless of whether the employee elects to contribute to the 401(k) Plan. For those Utility Workers Union of America (“UWUA”) Local 341 members who are hired on or after April 1, 2012, the Plan provides enhanced Plan benefits including the Company matching employee elective deferrals up to 6% of base pay and the Company contributing 4% of base pay each year, regardless of whether the employee elects to contribute to the 401(k) Plan. For those International Brotherhood of Electrical Workers (“IBEW”) members who are hired on or after June 1, 2012, and for IBEW members who elected to move from the Company’s existing Pension Plan and accept a frozen pension benefit, the Plan provides enhanced Plan benefits including the Company matching employee elective deferrals up to 6% of base pay and the Company contributing 4% of base pay each year, regardless of whether the employee elects to contribute to the 401(k) Plan. For those UWUA - Local B340 members who are hired on or after June 1, 2013, the Plan provides enhanced Plan benefits including the Company matching employee elective deferrals up to 6% of base pay and the Company contributing 4% of base pay each year, regardless of whether the employee elects to contribute to the 401(k) plan. For those Laborers’ International Union of North America (“LIUNA”) Local 327 members who are hired on or after January 1, 2010, the Plan provides enhanced Plan benefits including the Company contributing 4% of eligible compensation, as defined by the Plan, each year, regardless of whether or not the non-union employee elects to contribute to the 401(k) Plan. The Company also matches 100% of these employees’ elective deferrals up to 6% of compensation. Participant Accounts Each participant’s account is credited with the participant’s contribution and allocations of (a) the Company’s contribution and (b) Plan earnings. Allocations are based on participant earnings or account balances, as defined by the Plan Document. Each participant’s account is charged for the investment management fees charged by each mutual fund. Investment management fees are netted against the earnings of each fund through each fund's expense ratio. The benefit to which a participant is entitled is the benefit that can be provided from the participant’s vested account. Vesting Participants are immediately vested in their contributions and the Company contributions plus actual earnings or losses thereon. Notes Receivable from Participants Participants may borrow from their account balances a minimum of $1,000 up to a maximum equal to the lesser of $50,000, reduced by the highest outstanding loan balance during the preceding twelve-month period, or 50% of their vested account balance. Loan terms range from 1 to 5 years or up to 15 years for the purchase of a primary residence. The loans are secured by the balance in the participant’s account and bear interest at a rate that is fixed at the origination of the loan at the then prime rate plus one percent (1%). No more than two loans may be outstanding at any time. Principal and interest is paid ratably through payroll deductions. As of December 31, 2025, there are 244 loans to participants, maturing from 2026 to 2039 with interest rates ranging between 4.25% and 9.50%. Payment of Benefits On termination of service due to death, disability or retirement, a participant may elect to receive either a lump-sum amount equal to the value of the participant’s vested interest in his or her account, partial distribution of any portion of the account balance, or annual installments over a fixed number of calendar quarters or years. In-service distributions and hardship withdrawals are available to participants in accordance with the provisions of the Plan. Payments are generally received in cash. Participants may elect to receive in-kind distributions of employer securities. In-Kind Distributions One of the Plan’s investment options is the Unitil Corporation Stock Fund (comprised of Company shares and a money market fund). When receiving payment of benefits, a participant invested in the Unitil Corporation Stock Fund may elect to receive whole shares of stock (i.e. in-kind distributions), with any fractional shares, and the cash and cash equivalent portions of the underlying stock account, being distributed in cash. In 2025, the Plan had in-kind distributions of $15,790, which are included in Benefits Paid to Participants on the Statement of Changes in Net Assets Available for Benefits. Investment Options The Plan offers 35 investment portfolio or fund options consisting of registered investment companies (mutual funds); one pooled separate account (New York Life Anchor Account - Stable Value Fund); and the Unitil Corporation Stock Fund (comprised of Company shares and a money market fund). Participants may change their investment options daily, and all investments within the plan are participant-directed. Unitil Corporation Stock Fund (Unitil Corporation, no par value common stock) The Unitil Corporation Stock Fund (“Stock Fund”) is set up to hold common shares for the participants of the Plan and maintains liquidity in cash and cash equivalents to facilitate the timely settlement of participant transactions. Participants may allocate or withdraw their account balances between this fund and other funds without restrictions. The Stock Fund had approximately 3% and 4% in cash and cash equivalents, and 97% and 96% in Company stock at December 31, 2025, and December 31, 2024, respectively.

FAIR VALUE OF PLAN ASSETS (Tables)

12 Months Ended

Dec. 31, 2025

EBP 002 [Member]

EBP, Investment, Fair Value and NAV [Line Items]

Assets Measured at Fair Value on a Recurring Basis

Assets measured at fair value on a recurring basis as of December 31, 2025 and 2024 are as follows:


	Fair Value Measurements at Reporting Date Using
Description	Balance as of December 31,		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
2025
Registered Investment Companies	$	153,994,534	$	153,994,534	$	—	$	—
Common Stock Fund		11,552,966		11,552,966		—		—
Total Investments at Fair Value	$	165,547,500	$	165,547,500	$	—	$	—

2024
Registered Investment Companies	$	132,071,752	$	132,071,752	$	—	$	—
Common Stock Fund		12,120,800		12,120,800		—		—
Total Investments at Fair Value	$	144,192,552	$	144,192,552	$	—	$	—

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

- Definition

Tabular disclosure of fair value of investment held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), including, but not limited to, fair value measured at net asset value per share as practical expedient (NAV).

+ References

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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-8

Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477783/962-325-50-3

Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 45
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477509/962-325-45-6

+ Details

SCHEDULE OF ASSETS (HELD AT END OF YEAR)

12 Months Ended

Dec. 31, 2025

EBP 002 [Member]

EBP, Schedule of Asset Held for Investment [Line Items]

SCHEDULE OF ASSETS (HELD AT END OF YEAR)


SCHEDULE H, LINE 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)
December 31, 2025
Description of Investment Including Maturity Date, Rate of Interest, Collateral, Par or Maturity Value

Identity of Insurer, Borrower, Lessor or Similar Party	Type of Investment	Cost	Current Value
Investments at Fair Value:
Vanguard Instit Index	Registered Investment Company	**	$	23,115,772
JP Morgan Large Growth R6	"	**		20,104,237
American Balanced Fund R6	"	**		20,093,099
Invesco Growth & Income R6	"	**		5,229,768
The Investment Co of Amer R6	"	**		4,955,633
Invesco Value Opportunities R6	"	**		3,959,150
Dodge & Cox Income Fund	"	**		3,914,346
American EUPAC R6	"	**		3,614,657
PGIM Jennison Small Company R6	"	**		3,016,146
Principal High Yield Fund R6	"	**		2,896,715
Fid Advisor Mid Cap II Fund Z	"	**		2,478,731
Undiscovered Mgrs Behav Val R6	"	**		2,149,968
MFS Intntl Intrinsic Value R6	"	**		2,077,903
Loomis Sayles Core Plus Bond N	"	**		1,905,982
PIMCO Real Return Fund	"	**		1,781,723
Vanguard Total Int Idx Adm	"	**		1,710,500
American New World Fund R6	"	**		1,489,854
Vanguard Total Bd Mkt Ind Adm	"	**		1,246,173
Goldman Intl SC Insights R6	"	**		1,172,814
Cohen & Steers Inst Realty	"	**		985,013
Vanguard Mid Cap Index Adm	"	**		567,380
Vanguard Sm Cap Index Fd Adm	"	**		512,681
PIMCO Income Fund	"	**		212,452
Janus Henderson Enterprise (N)	"	**		57,817
JP Morgan US Govt MMkt Fund	"	**		40,849
Amer Target 2020 Fund R6	"	**		2,377,950
Amer Target 2025 Fund R6	"	**		4,165,647
Amer Target 2030 Fund R6	"	**		8,053,191
Amer Target 2035 Fund R6	"	**		4,130,552
Amer Target 2040 Fund R6	"	**		5,811,710
Amer Target 2045 Fund R6	"	**		5,914,450
Amer Target 2050 Fund R6	"	**		4,519,806
Amer Target 2055 Fund R6	"	**		7,554,615
Amer Target 2060 Fund R6	"	**		1,251,974
Amer Target 2065 Fund R6	"	**		925,276
PIMCO Money Market Fund Admin	"	**		402,902
* Unitil Corp Common Stock	Common Stock	**		11,150,064
Total Investments at Fair Value				165,547,500
Investments at Contract Value:
New York Life Stable Value Fund	Pooled Separate Account	**		9,815,758
Total Investments on Financial Statements				175,363,258
* Notes Receivable from Participants	Participant Loans - 4.25% - 9.50%	n/a		2,354,207
Total			$	177,717,465
* Represents a party-in-interest to the Plan
** Cost omitted for participant-directed investments

EMPLOYEE BENEFIT PLAN, STATEMENT OF CHANGES IN NET ASSETS AVAILABLE FOR BENEFITS - EBP 002 [Member]	12 Months Ended
	Dec. 31, 2025 USD ($)
Investment income:
Net appreciation in fair value of investments	$ 11,509,647
Interest and dividends	10,160,637
Total investment income	21,670,284
Interest on notes receivable from participants	193,870
Contributions:
Participant	6,788,312
Employer	5,112,494
Participant rollovers	1,914,836
Total contributions	13,815,642
Total additions	35,679,796
Deductions from net assets attributed to:
Benefits paid to participants	(6,521,230)
Rollover distributions	(7,469,957)
Administrative fees	(203,196)
Total deductions	(14,194,383)
Net increase	21,485,413
Net assets available for benefits:
Beginning of year	156,232,052
End of year	$ 177,717,465

FAIR VALUE OF PLAN ASSETS - Assets Measured at Fair Value on a Recurring Basis (Details) - EBP 002 [Member] - USD ($)	Dec. 31, 2025	Dec. 31, 2024
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	$ 165,547,500	$ 144,192,552
Registered Investment Companies [Member]
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	153,994,534	132,071,752
Common Stock Fund [Member]
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	11,552,966	12,120,800
Quoted Prices in Active Markets for Identical Assets (Level 1)
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	165,547,500	144,192,552
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Registered Investment Companies [Member]
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	153,994,534	132,071,752
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Common Stock Fund [Member]
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	11,552,966	12,120,800
Significant Other Observable Inputs (Level 2) \| Registered Investment Companies [Member]
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	0	0
Significant Other Observable Inputs (Level 2) \| Common Stock Fund [Member]
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	0	0
Significant Unobservable Inputs (Level 3) \| Registered Investment Companies [Member]
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	0	0
Significant Unobservable Inputs (Level 3) \| Common Stock Fund [Member]
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	$ 0	$ 0

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

SCHEDULE OF ASSETS (HELD AT END OF YEAR) (Details) - EBP 002 [Member]

12 Months Ended

Dec. 31, 2025

USD ($)

EBP, Schedule of Asset Held for Investment [Line Items]

Entity Tax Identification Number

02-0381573

EBP, Plan Number

002

EBP, Plan Name

Unitil Corporation Tax Deferred Savings and Investment Plan

EBP, Asset Held for Investment, Party-in-Interest [true false]

true

^[1]

Document and Entity Information	12 Months Ended
Document and Entity Information	Dec. 31, 2025
Cover [Abstract]
Document Type	11-K
Document Period End Date	Dec. 31, 2025
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2025
Document Fiscal Period Focus	FY
Entity Central Index Key	0000755001
Entity Registrant Name	UNITIL CORPORATION
Amendment Flag	false

PARTY-IN-INTEREST TRANSACTIONS (Additional Information) (Details) - EBP 002 [Member] - USD ($)	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
EBP, Related Party and Party-in-Interest Transactions [Line Items]
Administrative fees	$ 203,196
EBP, Trustee [Member]
EBP, Related Party and Party-in-Interest Transactions [Line Items]
Administrative fees	$ 203,196
EBP, Trustee [Member] \| Common Stock Fund [Member]
EBP, Related Party and Party-in-Interest Transactions [Line Items]
EBP, Number of Shares	230,183	214,949
EBP, Shares Value	$ 11,150,064	$ 11,648,086
EBP, Change in Value of Stock	$ 1,208,483

SUBSEQUENT EVENTS (Additional Information) (Details)	12 Months Ended
SUBSEQUENT EVENTS (Additional Information) (Details)	Dec. 31, 2025
EBP 002 [Member]
EBP, Subsequent Event [Line Items]
Employee Benefit Plan, Material Subsequent Event Affected or Non Affected the Plan	false

SUBSEQUENT EVENTS	12 Months Ended
SUBSEQUENT EVENTS	Dec. 31, 2025
EBP 002 [Member]
EBP, Subsequent Event [Line Items]
SUBSEQUENT EVENTS	NOTE I - SUBSEQUENT EVENTS The Plan has evaluated all events or transactions through the date of this filing. During this period, there were no material subsequent events which affected the Plan's financial statements.

PARTY-IN-INTEREST TRANSACTIONS	12 Months Ended
PARTY-IN-INTEREST TRANSACTIONS	Dec. 31, 2025
EBP 002 [Member]
EBP, Related Party and Party-in-Interest Transactions [Line Items]
PARTY-IN-INTEREST TRANSACTIONS	NOTE H - PARTY-IN-INTEREST TRANSACTIONS Included in the Plan’s assets are common shares of Unitil Corporation, the Plan’s sponsor, and notes receivable from participants. These transactions qualify as party-in-interest transactions. As of December 31, 2025 and 2024, there were 230,183 and 214,949 common shares, respectively, of Unitil Corporation, a gross value of $11,150,064 and $11,648,086, respectively, included in the Plan’s assets. During the year ended December 31, 2025, the Unitil Corporation common stock included in the Plan’s assets depreciated by $1,208,483. For the year ended December 31, 2025, $203,196 of administrative expenses were paid to John Hancock Trust Company directly from the Plan.

PLAN TERMINATION	12 Months Ended
PLAN TERMINATION	Dec. 31, 2025
EBP 002 [Member]
Employee Benefit Plan Plan Termination [Line Items]
PLAN TERMINATION	NOTE D - PLAN TERMINATION Although it has not expressed any intent to do so, the Company has the right under the Plan to terminate the Plan at any time subject to the provisions of ERISA with respect to its employees by a written resolution with a copy delivered to the Plan’s trustee. In the event of a Plan termination, participants would become fully vested in the balance of their accounts and the Plan assets would be distributed in accordance with the terms of the Plan Document.

RISKS AND UNCERTAINTIES	12 Months Ended
RISKS AND UNCERTAINTIES	Dec. 31, 2025
EBP 002 [Member]
EBP, Risk and Uncertainty [Line Items]
RISKS AND UNCERTAINTIES	NOTE C - RISKS AND UNCERTAINTIES The Plan provides for various investment options in any combination of stocks, fixed income securities, mutual funds and other investment securities. Investment securities are exposed to various risks, such as interest rate, market and credit risks. Due to the level of risk associated with certain investment securities, it is reasonably possible that changes in the values of investment securities will occur in the near term and that such changes could materially affect participants’ account balances and the amount reported in the Statements of Net Assets Available for Benefits.