The Cosmos Club was born on November 16, 1878, at the home of John Wesley Powell, distinguished geologist and explorer.
The first Clubhouse was located in rented rooms on the third floor of the Corcoran Building at the corner of 15th Street and Pennsylvania Avenue, N.W. From 1886 to 1952, the Club occupied several historic residences it owned on Lafayette Square, including the house that had been occupied by Dolley Madison.
In 1950, the Cosmos Club purchased the elegant mansion at 2121 Massachusetts Avenue, N.W. The central part of the building was constructed in 1873 by Curtis Justin Hillyer and acquired by Mary Scott Townsend (Mrs. Richard) in 1898. Between 1899 and 1900 the Townsends reconstructed the building and added two wings.
Before occupying its new home in 1952, the Club undertook a major renovation project, adding a dining room and kitchen area and an annex of sleeping rooms. What had been the stable and coach house were connected to the new dining area and turned into an auditorium. In 1960-1961, the Club added a first-floor bar, an expanded second-floor dining room, and three private meeting rooms and a Board room on the third floor.
In 1991, the Club completed a major expansion of the kitchen and dining rooms, added a bar, and created a new rear entrance. In 1997, the adjacent former French Military Mission (purchased by the Club in 1985) was renovated to become the Hillyer House, consisting primarily of overnight rooms and connected to the main mansion by a two-story bridge that includes sleeping rooms and offices.
In 2012, the second-floor Warne Ballroom was completely restored to its turn-of-the-twentieth century elegance. During the process, one of the original chandeliers was found and returned; it was paired with a copy made in France.
A multi-year renovation of the first floor was begun in 2015 with the restoration of one of the original parlors (now the Club Room) and the creation of a new reception area and enhanced hallway from the rear entrance. In 2017, major renovations of the dining room and kitchen were completed.
The Clubhouse is individually listed in the National Register of Historic Places and is designated as a District of Columbia Landmark.