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( Mark one ) UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , DC 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 TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from Corporate Office Properties Trust Commission file number 1-14023 ( Corporate Office Properties Trust ) Commission file number 333-189188 ( Corporate Office Properties , L.P. ) CORPORATE OFFICE PROPERTIES TRUST CORPORATE OFFICE PROPERTIES , L.P. ( Exact name of registrant as specified in its charter ) Corporate Office Properties , L.P. 6711 Columbia Gateway Drive , Suite 300 , Columbia , MD ( Address of principal executive offices ) Securities registered pursuant to Section 12 ( b ) of the Act : Title of each class Common Shares of beneficial interest , $ 0.01 par value Securities registered pursuant to Section 12 ( g ) of the Act : None or Maryland ( State or other jurisdiction of incorporation or organization ) Delaware Registrant's telephone number , including area code : ( 443 ) 285-5400 No No ( State or other jurisdiction of incorporation or organization ) to Trading Symbol ( s ) OFC Corporate Office Properties Trust Yes No Corporate Office Properties , L.P. Yes No Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Corporate Office Properties Trust Yes Corporate Office Properties , L.P. Yes 23-2947217 ( IRS Employer Identification No. ) 23-2930022 ( IRS Employer Identification No. ) 21046 ( Zip Code ) Name of each exchange on which registered New York Stock Exchange Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Exchange Act . Corporate Office Properties Trust Yes No Corporate Office Properties , L.P. Yes No 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 . Corporate Office Properties Trust > Yes No Corporate Office Properties , L.P. Yes No 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 ( or for such shorter period that the registrant was required to submit such files ) .