Built of adobe bricks in 1876, this is the third oldest surviving building at Fort Apache. Originally the Adjutant's Office, the administrative office of the post, it also served at various times as post headquarters, military post office, telegraph office, and post library. During the military period, the main entrance was on the west side facing the parade ground. Rehabilitated in 2001, it continues to serve Fort Apache and surrounding communities as the U.S. Post Office.