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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 For the fiscal year ended December 31 , 2020 OR TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from : to Commission file number : 1-13754 THE HANOVER INSURANCE GROUP , INC . ( Exact name of registrant as specified in its charter ) Delaware ( State or other jurisdiction of incorporation or organization ) Large accelerated filer Non - accelerated filer 440 Lincoln Street , Worcester , Massachusetts 01653 ( Address of principal executive offices ) ( Zip Code ) Title of each class Common Stock , $ .01 par value 7 5 / 8 % Senior Debentures due 2025 ( 508 ) 855-1000 ( Registrant's telephone number , including area code ) Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol THG THG 04-3263626 ( I.R.S. Employer Identification No. ) Name of each exchange on which registered New York Stock Exchange New York Stock Exchange Securities registered pursuant to Section 12 ( g ) of the Act : NONE Yes > No No 区 Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . 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 X 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 during the preceding 12 months . Yes > No □ 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 Smaller reporting company 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 . 000 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. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . No | Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Act ) . Yes □ Based on the closing sales price of June 30 , 2020 , the aggregate market value of the voting and non - voting common stock held by non - affiliates of the registrant was $ 3,814,120,782 . The number of shares outstanding of the registrant's common stock , $ 0.01 par value , was 36,387,389 shares as of February 19 , 2021 . DOCUMENTS INCORPORATED BY REFERENCE Portions of The Hanover Insurance Group , Inc.'s Proxy Statement to be filed pursuant to Regulation 14A relating to the 2021 Annual Meeting of Shareholders to be held May 11 , 2021 are incorporated by reference in Part III .