There are 3 US Post Offices in Mason County serving a total of 3,832 residents equating to 1,277 residents per post office. It's estimated that approximately 6,116 packages are handled across the 3 county post offices annually. Mason County is a county located on the Edwards Plateau in the U.S. state of Texas. At the 2010 census, its population was 4,012. Its county seat is Mason. The county is named for Fort Mason, which was located in the county."