Camp Cooper was on the Clear Fork of the Brazos River seven miles north of the site of present Fort Griffin State Historic Site in south central Throckmorton County. It was established by the Texas legislature in January 1856 and named for United States Army adjutant general Samuel Cooper. Its mission was to protect the frontier and to monitor the nearby Comanche Indian reservation. The area had been a campsite for three companies of the Fifth Infantry in 1851. The site was subsequently surveyed by Capt. Randolph B. Marcy and Robert S. Neighbors. The post was founded by Col. Albert Sidney Johnston in January 1856 and became headquarters for four companies of the Second United States Cavalry under the command of Lt. Col. Robert E. Lee. This was Lee's first command of a fort. He remained in charge for fifteen months, from April 9, 1856, until July 22, 1857. Captains under his command included Earl Van Dorn and Theodore O'Hara.
Although the camp initially had adequate military stores, it was plagued by severe weather, insects, dust, and irregular supply trains. Rattlesnakes were constant visitors, and Lee kept one as a pet. When he left the camp in 1857 for San Antonio, Maj. George H. Thomas took over. Thomas commanded the Cimarron expedition into Northwest Texas that same year. Troops from Camp Cooper participated in numerous campaigns and police actions against hostile Indians, including the pursuit of Peta Nocona's Comanches that resulted in the death of Peta Nocona and the recapture of Cynthia Ann Parker. Local unrest declined after 1859, when the Comanche reservation was dissolved and the Indians were removed from the area. During this same time Lt. Joseph F. Minter made a sketch of Cooper showing stone and picket buildings for the officers' quarters, hospital, and commissary. Enlisted men and the regimental band were quartered in barracks with shingle roofs and walls of mud bricks. A post office operated at the camp from March 31 to October 1860, but the coming of the Civil War brought an end to the camp's usefulness. The post was officially abandoned on February 21, 1861, and Capt. S. D. Carpenter surrendered the site to Col. W. C. Dalrymple four days later. By March all military activity at Camp Cooper had ceased.