On September 16, 1976, the Senate passed a resolution to name the reception room the Mike Mansfield Room, to honor the Montana senator upon his retirement. Mansfield served 24 years in the Senate, including four years as Democratic Party Whip and 16 years as majority leader.

Johnson Room, Senate Reception Room, the President's Room, the Committee on Naval Affairs room and the Senate Committee on Military Affairs room. Beginning in 1855, Constantino Brumidi decorated many walls and ceilings in the U.S. Capitol, most prominently in the Capitol Rotunda and the corridors of the Senate wing.

Originally intended for party caucuses, or meetings where members of the same party decided upon their candidates, policies, and legislative matters, the room has served as the stage for hearings on many important Senate committee investigations, including the Titanic, Pearl Harbor, and Watergate.

The fourth floor and the basement/terrace level of the Capitol are occupied by offices, machinery rooms, workshops, and other support areas.