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Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON , D.C. 20549 FORM 10 - K ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 OR For the transition period from New Hampshire ( State or other jurisdiction of incorporation or organization ) Title of each class Common Stock , no par value Commission file number 1-8858 UNITIL CORPORATION ( Exact name of registrant as specified in its charter ) 6 Liberty Lane West , Hampton , New Hampshire ( Address of principal executive offices ) to Registrant's telephone number , including area code : ( 603 ) 772-0775 Securities registered pursuant to Section 12 ( b ) of the Act : 02-0381573 ( I.R.S. Employer Identification No. ) 03842-1720 ( Zip Code ) Trading Symbol UTL Securities registered pursuant to Section 12 ( g ) of the Act : NONE Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes No Name of each exchange of which registered New York Stock Exchange Non - accelerated filer Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( §232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes No No No X Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See the definitions of " large accelerated filer " , " accelerated filer " , " smaller reporting company " and " emerging growth company " in Rule 12b - 2 of the Exchange Act . Accelerated filer Large accelerated filer > Emerging growth company Smaller reporting 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 Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 762 ( b ) ) by the registered public accounting firm that prepared or issued its audit report > Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Act ) . Yes No > Based on the closing price of the registrant's common stock on June 30 , 2020 , the aggregate market value of common stock held by non - affiliates of the registrant was $ 663,233,171 . The number of shares of the registrant's common stock outstanding was 15,013,542 as of January 29 , 2021 . Documents Incorporated by Reference : Portions of the Proxy Statement relating to the Annual Meeting of Shareholders to be held on April 28 , 2021 are incorporated by reference into Part III of this Report .