The Cosmos Club is at 2121 Massachusetts Avenue, in the heart of Embassy Row. The building is referred to as the Townsend Mansion, after the original owner, Mary Scott Townsend. It is one of the grand large townhouses near Dupont Circle, built in 1900. The townhouse is in the Beaux-Arts style, and was designed by architects John Merven Carrère and Thomas Hastings, who also designed the Cannon House Office Building, the Russell Senate Office Building, and the Carnegie Institution in D.C., and the New York Public Library.
The Cosmos Club purchased the building in 1950. The Cosmos Club was founded in 1878, for men in the arts and sciences. Women could first become members 110 years later.