The headquarters building was built on Grierson's orders in 1876, a decade into the fort's military operation. The building is U-shaped, opening to the east, with two chimneys in the main structure and one in the north and south wings. A veranda is attached to the façade and back of the building, between the wings. The headquarters building was used in various capacities in the 20 years after the US Army left Fort Concho. Four of the rooms on the ground floor, the court martial, orderly's room, adjutant's office, and regimental headquarters, have been remodeled to appear as they would have during the fort's military career. About of the headquarters building is the former residence of Oscar Ruffini, San Angelo's first civic architect. The house was moved to its present location on May 14, 1951.