The Corcoran Gallery of Art, diagonally opposite the State, War and Navy Building and a few hundred feet southwest of the White House, was chartered in 1870 by William Wilson Corcoran, a Washington banker and philanthropist. It was his purpose to honor American art and to encourage American artists. In 1874 he housed the collection at Seventeenth Street and Pennsylvania Avenue in the building now occupied by the United States Court of Claims In the rooms were hung pictures by American artists in whom Corcoran took particular pride--such men as Cole, Inness, Peale, and Sully--and among the Europeans were works by Gérôme, Mengs, and Scheffer. In addition to paintings, there five pieces of sculpture, including The Greek Slave by Powers. From this nucleus, the Corcoran collection was increased during the during the last years of the founder's life and continuously thereafter through purchases from the trust fund he established. He made an additional gift to American art in founding a free art school which in operated in connection with the gallery.
In 1891 the trustees of the gallery commissioned Ernest Flagg to design a new building, into which they installed the collection 6 years later. These quarters were sufficient until the transfer of the Clark collection in 1926 necessitated further expansion. A new wing, provided by the family of William Andrews Clark for the separate housing of the collection, and designed by Charles A. Platt, was opened to public in 1927...
The Corcoran Gallery of Art is an example of late nineteenth century neoclassic architecture, based upon Greek precedent in the treatment of its details. The building is ponderous and undistinguished in its mass; and the suggestion that its form resembles an ancient sarcophagus is not altogether amiss. The windows of the high rusticated base, and the heavy stone grille below the frieze and cornice, tend in some degree to relieve the severity of the facade.
The exterior, which is constructed of white Georgia marble with a basement story of pink granite, consists of a large central section flanked by end pavilions. The large north pavilion is designed as a semicircular bay and contains the offices and studios of the Corcoran School of Art, entered from the New York Avenue side of the Building. A large section containing the Clark collection adjoins the main structure on the west.
-Washington, City and Capital, 1937, pg. 382-391.
The above quote comes from a 10 page section on the Corcoran Gallery of Art. The Gallery continues to operate from the building listed in the Guide. The State, War and Navy Building mentioned was known as the Old Executive Office Building, now known as Eisenhower Executive Office Building.
The gallery is the largest privately supported cultural institute in Washington. The museum's main focus continues to be American art but does have many works by European masters in its collection.