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

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.

Indicate by check mark whether the registrant: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

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

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. 7262(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

The aggregate market value of the voting and non-voting shares of common stock held by non-affiliates of Corporate OfficeCOPT Defense Properties Trust was approximately $2.8$2.3 billion, as calculated using the closing price of such shares on the New York Stock Exchange as of and the number of outstanding shares as of June 30, 2021.2023. For purposes of calculating this amount only, affiliates are defined as Trustees, executive owners and beneficial owners of more than 10% of Corporate Office Properties Trust’sCOPT Defense Properties’ outstanding common shares, $0.01 par value. At February 7, 2022, 112,319,9822024, 112,548,467 of Corporate Office Properties Trust’sCOPT Defense Properties’ common shares were outstanding.

Portions of the proxy statement of Corporate OfficeCOPT Defense Properties Trust for its 20222024 Annual Meeting of Shareholders to be filed within 120 days after the end of the fiscal year covered by this Form 10-K are incorporated by reference into Part III of this Form 10-K.

This Form 10-K contains “forward-looking” statements, as defined in the Private Securities Litigation Reform Act of 1995, that are based on our current expectations, estimates and projections about future events and financial trends affecting the financial condition and operations of our business. Additionally, documents we subsequently file with the SEC and incorporated by reference will contain forward-looking statements.

Forward-looking statements can be identified by the use of words such as “may,” “will,” “should,” “could,” “believe,” “anticipate,” “expect,” “estimate,” “plan” or other comparable terminology. Forward-looking statements are inherently subject to risks and uncertainties, many of which we cannot predict with accuracy and some of which we might not even anticipate. Although we believe that the expectations, estimates and projections reflected in such forward-looking statements are based on reasonable assumptions at the time made, we can give no assurance that these expectations, estimates and projections will be achieved. Future events and actual results may differ materially from those discussed in the forward-looking statements. We caution readers that forward-looking statements reflect our opinion only as of the date on which they were made. You should not place undue reliance on forward-looking statements. The following factors, among others, could cause actual results and future events to differ materially from those set forth or contemplated in the forward-looking statements:

We conduct almost all of our operations and own almost all of our assets through our operating partnership, Corporate OfficeCOPT Defense Properties, L.P. (“COPLP”CDPLP”) and subsidiaries (collectively, the “Operating Partnership”), of which COPT Defense is the sole general partner. COPLPCDPLP owns real estate directly and through subsidiary partnerships and limited liability companies (“LLCs”).  In addition to owning real estate, COPLPCDPLP also owns subsidiaries that provide real estate services such as property management, development and construction services primarily for our properties but also for third parties. Some of these services are performed by a taxable REIT subsidiary (“TRS”). In September 2023, we changed CDPLP’s name from Corporate Office Properties, L.P. to COPT Defense Properties, L.P.

Equity interests in COPLPCDPLP are in the form of common and preferred units. As of December 31, 2021,2023, COPT Defense owned 98.3%97.8% of the outstanding COPLPCDPLP common units (“common units”) and there were no preferred units outstanding. Common units not owned by COPT Defense carry certain redemption rights. The number of common units owned by COPT Defense is equivalent to the number of outstanding common shares of beneficial interest (“common shares”) of COPT Defense, and the entitlement of common units to quarterly distributions and payments in liquidation is substantially the same as that of COPT Defense common shareholders.

COPT’sIn September 2023, the ticker symbol under which our common shares are publicly traded on the New York Stock Exchange (“NYSE”) under the ticker symbolchanged from “OFC” to “CDP”.

We believe that COPT Defense is organized and has operated in a manner that satisfies the requirements for taxation as a REIT under the Internal Revenue Code of 1986, as amended, and we intend to continue to operate COPT Defense in such a manner. If COPT Defense continues to qualify for taxation as a REIT, it generally will not be subject to Federalfederal income tax on its taxable income (other than that of its TRS entities) that is distributed to its shareholders. A REIT is subject to a number of organizational and operational requirements, including a requirement that it distribute at least 90% of its annual taxable income to its shareholders.

Our executive offices are located at 6711 Columbia Gateway Drive, Suite 300, Columbia, Maryland 21046 and our telephone number is (443) 285-5400.

Our Internet address is www.copt.com. We make available on our Internet website free of charge our annual reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K and amendments to those reports filed or furnished pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), as soon as reasonably possible after we file such material with the Securities and Exchange Commission (the “SEC”). In addition, we have made available on our Internet website under the heading “Corporate Governance” the charters for our Board of Trustees’ Audit, Nominating and Corporate Governance, Compensation and Investment Committees, as well as our Corporate Governance Guidelines, Code of Business Conduct and Ethics and Code of Ethics for Financial Officers. We intend to make available on our website any future amendments or waivers to our Code of Business Conduct and Ethics and Code of Ethics for Financial Officers within four business days after any such amendments or waivers. The information on our Internet site is not part of this report.

The SEC maintains an Internet website that contains reports, proxy and information statements and other information regarding issuers that file electronically with the SEC. This Internet website can be accessed at www.sec.gov.

In recent years,Our Defense/IT Portfolio includes data center shells, have been a growth driver for our Defense/IT Locations. Data center shellswhich are properties leased to tenants to be operated as data centers in which we provide tenants with only the core building and basic power, while the tenants fund the costs for the critical power, fiber connectivity and data center infrastructure.  From 2013 through 2021, we placed into service 26 data center shells totaling 4.7 million square feet, and we had an additional three under development totaling 685,000 square feet as of December 31, 2021.  We enter into long-term leases for these properties prior to commencing development, with triple-net structures, rent escalators and multiple extension options and rent escalators.options. Additionally, our tenants’ significant funding of the costs to fully power and equip these properties significantlygreatly enhances the value of these properties and creates high barriers to exit for such tenants.

We believe that our properties and teamcross-discipline teams collectively complement our Defense/IT Locations strategy due to our:to:

We aim to sustainably develop and operate our portfolio to create healthier work environments and reduce consumption of resources by: (1) developing new buildings designed to use resources with a high level of efficiency and low impact on human health and the environment during their life cycles through our participation in the U.S. Green Building Council’s Leadership in Energy and Environmental Design (“LEED”) program, (targetingtargeting new office properties to meet or exceed LEED Silver certification standards or, when not possible, striving to otherwise incorporate LEED criteria into property designs);designs; (2) adopting select LEED for Building Operations and Maintenance (“LEED O+M: Existing Buildings”) guidelines for much of our portfolio, including cleaning, recycling, and energy reduction and landscaping practices; (3) investing in building automation systems and otherhigh-efficiency heating and air conditioning equipment thatand implementing resource conservation practices to reduce energy consumption; (4) investing in water saving features, such as low-flow toilets and sensor-activated sinks;water-saving features; and (5) participating in the annual Global Real Estate Sustainability Benchmark (“GRESB”) survey, which is widely recognized for measuring the environmental, social and governance (“ESG”) performance of real estate companies and funds. We earned an overall score of “Green Star” on the GRESB survey in each of the last sevennine years, representing the highest quadrant of achievement on the survey.

As of December 31, 2021,2023, our operations included the following reportable segments: Defense/IT Locations; Regional Office; Wholesale Data Center;Portfolio and Other. Our Defense/IT LocationsPortfolio segment included the following sub-segments:

For information relating to our reportable segments, refer to Note 1613 to our consolidated financial statements, which are included in a separate section at the end of this Annual Report on Form 10-K beginning on page F-1.

We operate in markets in which we compete for human capital. We rely on our employees to drive our success and we support them with a variety of programs to enhance their workplace engagement and job fulfillment.

We believe in equal opportunity, engagement and ethics. All employees must adhere to our Code of Business Conduct. We typically survey our workforce annually to measure engagement, use the feedback to enhanceemployee engagement and identify opportunities for further improvement, which we believe that this has helped us to achieve annual “best workplace” honors for over a decade.

Safety is a key part of our employee wellbeing, largely weighted in the Physical pillar.dimension. Recognizing this, we conduct job-tailored safety training on an ongoing basis. We also monitor our workers’ compensation claims to measure the effectiveness of our safety program.

We offer robust learning programs to all employees, including educational assistance for college-level and vocational degree programs, and cover all expenses for licenses and certifications, management and leadership courses, key skills training and industry and professional conferences. Further, we offer internship and mentorship programs to facilitate teaching and learning from others.

We also compete with manyother entities, including other publicly-traded commercial office REITs, for capital. This competition could adversely affect our ability to raise capital that we may need to fulfill our capital strategy.

In addition, we compete with manyother entities for talent. If there is an increase in the costs for us to retain employees, or if we otherwise fail to attract and retain such employees, our business and operating results could be adversely effected.affected.

Set forth below are risks and uncertainties relating to our business and the ownership of our securities. These risks and uncertainties may lead to outcomes that could adversely affect our financial position, results of operations, cash flows or ability to make expected distributions to our shareholders. You should carefully consider each of these risks and uncertainties, along with all of the information in this Annual Report on Form 10-K and its Exhibits, including our consolidated financial statements and notes thereto for the year ended December 31, 20212023 included in a separate section at the end of this report beginning on page F-1.

For new tenants or upon expiration of existing leases, we generally must make improvements and pay other leasing costs for which we may not receive increased rents. We also make building-related capital improvements for which tenants may not reimburse us.

If our properties do not generate revenue sufficient to meet our operating expenses and capital costs, we may need to borrow additional amounts to cover these costs. In such circumstances, we would likely have lower profits or possibly incur losses. We may also find in such circumstances that we are unable to borrow to coverfund such costs, in which case our operations could be adversely affected.

In addition, the competitive environment for leasing is affected considerably by a number of factors including, among other things, changes due to economic factors such as supply and demand. These factors may make it difficult for us to lease existing vacant space in existing properties or newly-developed properties and space associated with future lease expirations at rental rates that are sufficient to meet our short-term capital needs.

Most of our leases with the USG provide for one-year terms, with a series of one-year terms.renewal options. The USG may terminate its leases if, among other reasons, the United States Congress fails to provide funding. We would be harmed if any of our largest tenants fail to make rental payments to us over an extended period of time, including as a result of a prolonged government shutdown, or if the USG elects to terminate some or all of its leases and the space cannot be re-leased on satisfactory terms.

As of December 31, 2021, 87.5%2023, 89.8% of our office and data center shell properties’ total annualized rental revenue was from our Defense/IT Locations, and we expect to maintain a similarly high revenue concentration from properties in these locations.Portfolio. A reduction in government spending targeting the activities of the government andUSG or its contractors (such as knowledge- and technology-based defense and security activities) in these locationsthis portfolio’s demand drivers could adversely affect our tenants’ ability to fulfill lease obligations, renew leases or enter into new leases and limit our future growth from properties in these locations. Moreover,whose demand rely on such activities. In addition, uncertainty regarding the potential for future reduction in government spending targetingfor such activities could also decrease or delay leasing activity from existing or new tenants engaged in these activities. Moreover, we may face additional economic harm in the event of long-term displacement, or elimination, of government spending for defense installations or missions from which demand for our Defense/IT Portfolio’s properties is driven.

We may pursue selective acquisitions of properties in regions where we have not previously owned properties. These acquisitions may entail risks in addition to those we face with acquisitions in more familiar regions, such as our not sufficiently anticipating conditions or trends in such regions and therefore not being able to operate the acquired properties profitably.

In addition, we may acquire properties that are subject to liabilities in situations where we have no recourse, or only limited recourse, against the prior owners or other third parties with respect to unknown liabilities. As a result, if a liability were asserted against us based upon ownership of those properties, we might have to pay substantial sums to settle or contest it. Examples of unknown liabilities with respect to acquired properties include, but are not limited to:

Although most of our properties have been subject to varying degrees of environmental assessment, many of these assessments are limited in scope and may not include or identify all potential environmental liabilities or risks associated with the property.  Identification of new compliance concerns or undiscovered areas of contamination, changes in the extent or known scope of contamination, discovery of additional sites, human exposure to the contamination or changes in cleanup or compliance requirements could result in significant costs to us.

We often use our Revolving Credit Facility to initially finance much of our investing activities and certain financing activities. Our lenders under this and other facilities could, for financial hardship or other reasons, fail to honor their commitments to fund our requests for borrowings under these facilities. If lenders default under these facilities by not being able or willing to fund a borrowing request, it would adversely affect our ability to access borrowing capacity under these facilities.

If interest rates were to rise, our debt service payments on debt with variable interest rates would increase.

Our operations likely will not generate enough cash flow to repay all of our debt without additional borrowings, equity issuances and/or property sales.sales of interests in properties. If we cannot refinance, extend the repayment date of, or otherwise raise funds required to repay, debt by its maturity date, we would default on such debt.

Our organizational documents do not limit the amount of indebtedness that we may incur. Therefore, we may incur additional indebtedness and become more highly leveraged, which could harm our financial position.

We have preventative, detective, and responsive measures in place to maintain the security and integrity of our networks and related systems that have to date enabled us to avoid breaches and disruptions that were individually, or in the aggregate, material. We also have insurance coverage in place in the event of significant future losses from breaches and disruptions. However, despite our activities to maintain the security and integrity of our networks and related systems, there can be no absolute assurance that these activities will be effective in mitigating these risks. We also have insurance coverage in place in the event of significant future losses from breaches and disruptions; however, continuing changes in the insurance industry’s risk assessment approach and pricing structure could in the future increase the cost for us to obtain insurance coverage or decrease the scope of such coverage available to us.

Like other businesses, we and our vendors and service providers have been, and expect to continue to be, subject to cyber-attacks or -intrusions, computer viruses or malware, attempts at unauthorized access and other events of varying degrees. A security breach or other significant disruption involving our IT networks and related systems, could disrupt our operations in numerous ways, including compromising the confidential informationor those of certain of our tenants, customers, vendors and employees, which could damage our relationships with such parties, and disruptingor service providers, could:

Subject to the requirements of the New York Stock Exchange, our Board of Trustees has the authority, without shareholder approval, to issue additional securities on terms that could delay or prevent a change in control. In addition, our Board of Trustees has the authority to reclassify any of our unissued common shares into preferred shares. Our Board of Trustees may issue preferred shares with such preferences, rights, powers and restrictions as our Board of Trustees may determine,if it chooses to do so, which could also delay or prevent a change in control.

In addition, various Maryland laws may have the effect of discouraging offers to acquire us, even if the acquisition would be advantageous to shareholders. Resolutions adopted by our Board of Trustees and/or provisions of our bylaws exempt us from

If COPT Defense fails to qualify as a REIT, it would be subject to Federalfederal income tax at regular corporate rates. Also, unless the Internal Revenue Service granted us relief under certain statutory provisions, COPT Defense would remain disqualified from being a REIT for four years following the year it first fails to qualify. If COPT Defense fails to qualify as a REIT, it would have to pay significant income taxes and would therefore have less money available for investments or for distributions to our shareholders. In addition, if COPT Defense fails to qualify as a REIT, it would no longer be required to pay distributions to shareholders. As a result of all these factors, COPT’sCOPT Defense’s failure to qualify as a REIT could impair our ability to expand our business and raise capital and would likely have a significant adverse effect on the value of our shares.

Occasionally, changes in state and local tax laws or regulations are enacted that may result in an increase in our tax liability. Shortfalls in tax revenues for states and municipalities may lead to an increase in the frequency and size of such changes. If such changes occur, we may be required to pay additional taxes on our assets, revenue or income.

The following table provides certain information about our operating property segments as of December 31, 20212023 (dollars and square feet in thousands, except per square foot amounts):

The following table provides certain information about office and data center shell properties that were under, or otherwise approvedcontractually committed for, development as of December 31, 20212023 (dollars and square feet in thousands):

The following table provides certain information about land that we owned or controlled as of December 31, 2021,2023, including properties under ground lease to us (square feet in thousands):

Lease Expirations

The following table provides a summary schedule of lease expirations for leases in place at our operating properties as of December 31, 20212023 based on the non-cancelable term of tenant leases determined in accordance with generally accepted accounting principles (dollars and square feet in thousands, except per square foot amounts):

We are not currently involved in any material litigation nor, to our knowledge, is any material litigation currently threatened against us (other than routine litigation arising in the ordinary course of business, substantially all of which is expected to be covered by liability insurance).

Not applicable.

The graph and the table set forth below assume $100 was invested on December 31, 20162018 in our common shares. The graph and the table compare the cumulative return (assuming reinvestment of dividends) of this investment with a $100 investment at that time in the S&P 500 Index, or the FTSE All Equity REITREITs Index of the National Association of Real Estate Investment Trusts (“Nareit”) (the “All Equity REITs Index”) and the Office Property Sector of the FTSE All Equity REITs Index of Nareit (the “Office Sector Index”):

You should refer to our consolidated financial statements and the notes thereto as you read this section.

This section contains “forward-looking” statements, as defined in the Private Securities Litigation Reform Act of 1995, that are based on our current expectations, estimates and projections about future events and financial trends affecting the financial condition and operations of our business. Forward-looking statements can be identified by the use of words such as “may,” “will,” “should,” “could,” “believe,” “anticipate,” “expect,” “estimate,” “plan” or other comparable terminology. Forward-looking statements are inherently subject to risks and uncertainties, many of which we cannot predict with accuracy and some of which we might not even anticipate. Although we believe that the expectations, estimates and projections reflected in such forward-looking statements are based on reasonable assumptions at the time made, we can give no assurance that these expectations, estimates and projections will be achieved. Future events and actual results may differ materially from those discussed in the forward-looking statements. Important factors that may affect these expectations, estimates and projections include, but are not limited to:

We leased 3.9 million square feetStrong demand from our Defense/IT Portfolio drove increased property occupancy that more than offset the continuing effects of lagging demand in 2021, representing our fifth consecutive year with leasingOther segment. Our strengthened operating property occupancy in excess of 3.0 million. This leasing included:2023 included increases in:

Defense/IT Portfolio demand also continued to feed growth in theour portfolio through property development. In 2023, our Defense/IT Portfolio:

We believe that our 2021 leasingDefense/IT Portfolio has strongly benefited from a continued:

As of December 31, 2021,2023, we had scheduled lease expirations for 1.62.6 million square feet in 2022,2024, representing 8.2%11.5% of our total occupied square feet and 9.4%12.8% of our total annualized rental revenue, from office and data center shells, including:

In 2021,On January 10, 2023, we refinanced mostraised $190.2 million in capital from our sale of a 90% interest in three data center shell properties in Northern Virginia, resulting in a gain on sale of $49.4 million. We retained a 10% interest in the properties through a newly-formed joint venture. We used substantially all of the proceeds from this sale to pay down our debt by issuing $1.4 billion in unsecured senior notes, including:Revolving Credit Facility to create additional borrowing capacity available to fund future development.

Due to the collective effectFor our 2023 results of our 2021 activity, we ended the year with:operations:

We refer to the measures “annualized rental revenue” and “tenant retention rate” in various sections of the Management’s Discussion and Analysis of Financial Condition and Results of Operations section of this Annual Report on Form 10-K. Annualized rental revenue is a measure that we use to evaluate the source of our rental revenue as of a point in time. It is

We also refer to the measures “cash rents”, “straight-line rents”, and “committed costs” in the “Occupancy and Leasing” section of the Management’s Discussion and Analysis of Financial Condition and Results of Operations section of this Annual Report on Form 10-K. Cash rents include monthly contractual base rent (ignoring rent abatements and rent associated with tenant funded landlord assets) multiplied by 12, plus estimated annualized expense reimbursements (as(average for first 12 months of lease commencementterm for new or renewed leases or as of lease expiration for expiring leases). Straight-line rents includesinclude annual minimum base rents, net of abatements and lease incentives and excluding rent associated with tenant funded landlord assets, on a straight-line basis over the term of the lease, and estimated annual expense reimbursements (as of lease commencement for new or renewed leases or as of lease expiration for expiring leases). We believe that cash rents and straight-line rents are useful measures for evaluating the rental rates of our leasing activity, including changes in such rates relative to rates that may have been previously in place, with cash rents serving as a measure to evaluate rents at the time rent payments commence, and straight-line rents serving as a measure to evaluate rents over the related lease terms. Committed costs includes tenant improvement allowances (excluding tenant funded landlord assets), leasing commissions and estimated turn key costs and excludes lease incentives; we believe this is a useful measure for evaluating our costs associated with obtaining new leases.

Our consolidated financial statements are preparedThe following table provides a summary schedule of lease expirations for leases in place at our operating properties as of December 31, 2023 based on the non-cancelable term of tenant leases determined in accordance with GAAP,generally accepted accounting principles (dollars and square feet in thousands, except per square foot amounts):

We are not currently involved in any material litigation nor, to our knowledge, is any material litigation currently threatened against us (other than routine litigation arising in the ordinary course of business, substantially all of which require usis expected to make certain estimatesbe covered by liability insurance).