The national headquarters of the Organization of American Historians at 112 North Bryan Avenue in Bloomington, Indiana (map) is located on the eastern edge of the Indiana University campus in a Georgian style brick house with an elaborate, classical portico. Known as "Raintree House" because of two former raintrees (Koelreuteria paniculata), one of which is the largest of its species in southern Indiana, the house stands on what is left of the 160 acres purchased in 1839 by Ellen and William Millen for $1,600. The remaining acres and house are now valued at approximately $250,000.
Built in 1845 from locally produced brick and virgin walnut timber, the house has yellow poplar floors and walnut woodwork. Raintree House is designated an Indiana historic site. The house's interior brick walls remain structurally unaltered, and it is furnished with numerous antiques.
Over the years Raintree House has changed hands many times. Between 1882 and 1925 it was owned and occupied by various members of a prominent Bloomington family, the Rogerses. From 1925 until 1944 it was owned by Agnes Wells, Indiana University Dean of Women, who called it "Wellswood House" after herself and a friend. Between 1944 and 1946, the property was owned by Geneva L. Graeba. Purchased by the Trustees of Indiana University in 1946, it was rented to university personnel and students until 1950 when Anna and Newton Stallknecht bought the house and property, refurbished the interior, and planted an elaborate but informal garden. In 1969 "Stallknect House" was sold to the Indiana University Foundation and renamed "Raintree House." As a result of a generous agreement negotiated by IU Chancellor Herman B Wells and former OAH Executive Secretary and IU History Professor Thomas D. Clark, the OAH executive offices have occupied historic Raintree House since 1970.
The house, also known as the "Millen House," was federally approved on the National Register of Historic Places, September 29, 2004.