District of Columbia-Maryland Reunion Act This bill cedes the District of Columbia to Maryland after Maryland's acceptance of the retrocession. Furthermore, the bill declares that the National Capital Service Area in the District shall not be ceded and relinquished to Maryland and shall continue to serve as the permanent seat of the federal government. The bill maintains the exclusive legislative authority and control of Congress over the area. Finally, excluding the District Building, the area shall include the principal federal monuments, the White House, the U.S. Capitol, the U.S. Supreme Court Building, the federal executive, legislative, and judicial office buildings located adjacent to the Mall and the U.S. Capitol, including any federal real property affronting or abutting such area, such as the Department of Housing and Urban Development and the Department of Energy buildings.