There are 4 US Post Offices in Mills County serving a total of 4,691 residents equating to 1,173 residents per post office. It's estimated that approximately 7,487 packages are handled across the 4 county post offices annually. Mills County is a county located on the Edwards Plateau in Central Texas. As of the 2010 census, its population was 4,936. The county seat is Goldthwaite. The county is named for John T. Mills, a justice of the Texas Supreme Court.