# EDGAR Filing Document

**Accession Number:** 0000755001
**File Stem:** 0001193125-25-324977
**Filing Date:** 2025-12
**Character Count:** 4791
**Document Hash:** 098e5eed9f9bd48116fa416cd89b94fb
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-25-324977.hdr.sgml**: 20251218

**ACCESSION NUMBER**: 0001193125-25-324977

**CONFORMED SUBMISSION TYPE**: 8-K

**PUBLIC DOCUMENT COUNT**: 12

**CONFORMED PERIOD OF REPORT**: 20251215

**ITEM INFORMATION**: Regulation FD Disclosure

**ITEM INFORMATION**: Other Events

**FILED AS OF DATE**: 20251218

**DATE AS OF CHANGE**: 20251218

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** UNITIL CORP
- **CENTRAL INDEX KEY:** 0000755001
- **STANDARD INDUSTRIAL CLASSIFICATION:** ELECTRIC & OTHER SERVICES COMBINED [4931]
- **ORGANIZATION NAME:** 01 Energy & Transportation
- **EIN:** 020381573
- **STATE OF INCORPORATION:** NH
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** 8-K
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-08858
- **FILM NUMBER:** 251583682

**BUSINESS ADDRESS:**
- **STREET 1:** 6 LIBERTY LANE WEST
- **CITY:** HAMPTON
- **STATE:** NH
- **ZIP:** 03842
- **BUSINESS PHONE:** 6037736504

**MAIL ADDRESS:**
- **STREET 1:** 6 LIBERTY LANE WEST
- **CITY:** HAMPTON
- **STATE:** NH
- **ZIP:** 03842

?xml version='1.0' encoding='ASCII'? 8-K

### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

#### Washington, D.C. 20549

### FORM 8-K

#### CURRENT REPORT

#### Pursuant to Section 13 or 15(d)

#### of the Securities Exchange Act of 1934

#### Date of Report (Date of earliest event reported): December 15, 2025

## UNITIL CORPORATION

#### (Exact name of registrant as specified in its charter)

---

| | | |
|:---|:---|:---|
| **New Hampshire** | **1-8858** | **02-0381573** |
| **(State or other jurisdiction** | **(Commission** | **(IRS Employer** |
| **of incorporation)** | **File Number)** | **Identification No.)** |

---

---

| | |
|:---|:---|
| **6 Liberty Lane West, Hampton, New Hampshire** | **03842-1720** |
| **(Address of principal executive offices)** | **(Zip Code)** |

---

#### Registrant's telephone number, including area code: (603) 772-0775

#### N/A

#### (Former name or former address, if changed since last report)
Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

---

| | | |
|:---|:---|:---|
| **Title of each class** | **Trading<br>Symbol** | **Name of each exchange**<br> **of which registered** |
| Common Stock, no par value | UTL | New York Stock Exchange |

---

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

------

#### Item 7.01 Regulation FD Disclosure
On December 15, 2025, Sandra L. Whitney, Corporate Secretary of Unitil Corporation (the "Company"), provided notice that she will retire and, in connection with her retirement, resign from the Company and each of its subsidiaries, effective as of the end of the day on December 31, 2025.

As part of the Company's ongoing succession plan, the Company will appoint Carleton B. Simpson as Corporate Secretary of the Company, effective as of January 1, 2026. Mr. Simpson is currently Senior Vice President and General Counsel of the Company. He will continue in that role in addition to becoming the Corporate Secretary of the Company.

The Company anticipates that Ms. Whitney will provide consulting services to the Company until April 30, 2026, to help with the transition of duties.

#### Item 8.01 Other Events
The first two paragraphs of Item 7.01 are incorporated by reference into this Item 8.01.

------

#### SIGNATURES
Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

---

| | |
|:---|:---|
| UNITIL CORPORATION | UNITIL CORPORATION |
| By: | /s/ Daniel J. Hurstak |
|  | Name: Daniel J. Hurstak |
|  | Title: Senior Vice President, Chief Financial Officer and Treasurer |

---

Date: December 18, 2025