Fort Mason functioned as a United States Army cavalry post in the Texas Hill Country, established in 1851 to open new territory for settlement and protect settlers from raids by Comanche, Kiowa, and Lipan Apache groups as the frontier line pushed westward after Texas statehood. The post is best known for housing the headquarters of the Second United States Cavalry Regiment from 1856 to 1861, a unit that assembled an unusually large number of officers who later became prominent Civil War generals on both sides, roughly a dozen for the Confederacy and several for the Union. Robert E. Lee served at Fort Mason as second-in-command of the Second Cavalry before the war, and the post is closely associated with his time in Texas. Soldiers stationed there patrolled the surrounding hill country, escorted travelers and supply routes, and responded to raids on outlying ranches, gradually pushing Native American groups farther from the expanding line of settlement. The Army abandoned the post after Texas seceded, and the buildings were later dismantled or fell into disrepair, with local residents salvaging much of the stone. In 1975 the Mason County Historical Society began reconstructing an officers' quarters building using surviving original materials on the original fort site. Today that reconstructed structure serves as a small museum and city park in Mason, preserving artifacts and interpreting the fort's frontier military history.