Erected in 1870, and built of limestone quarried from a nearby hill, the Post Headquarters building housed the administrative offices. The Commanding Officer, his executive officer, the adjutant, a sergeant and a signal officer worked here. The adjutant had the authority to execute an order if the Commanding Officer was absent. One of the rooms was used for the Post Library to hold the few periodicals and books that might be shipped from back East. After close of business hours, the Guardhouse became the Post Headquarters for any business that needed to be dealt with or transacted.
In October of 1873, Governor Davis of Texas held a council here and freed Kiowa chiefs Satanta and Big Tree. In July of 1901 29,000 homesteaders gathered at the Headquarters to register for the opening of the Kiowa, Comanche and Apache Reservation. Captain Dan T. Moore moved the headquarters of the Field Artillery School to the more spacious old post headquarters building when it was vacated by the post commander upon completion of the new post in the fall of 1911. In 1912, the school moved to one of the new unoccupied barracks in the new post area. From 1913-1918 the School of Musketry was here. The Ordnance Department took over and had its offices here until World War II. It is presently used as the Museum's Headquarters.