Mason County is a rural county located on the Edwards Plateau in the U.S. state of Texas. At the 2020 census, its population was 3,953. Its county seat is Mason. The county is named for Fort Mason, which was located in the county.

Fort Mason was established on July 6, 1851, in present-day Mason County, Texas. It was named in honor of George Thomson Mason, a United States Army second lieutenant killed in the Thornton Affair during the Mexican–American War near Brownsville, April 25, 1846. At various times from 1856 to 1861, this was the home fort for Albert Sidney Johnston, George H. Thomas, Earl Van Dorn, and Robert E. Lee. The fort was abandoned by the military in the 1870s, and restored by a group of local citizens in 1975. Visitors can tour the reproduction officers' quarters at the Fort Mason Museum.