There are 6 US Post Offices in Hays County serving a total of 160,287 residents equating to 26,715 residents per post office. It's estimated that approximately 255,836 packages are handled across the 6 county post offices annually. Hays County is a county located on the Edwards Plateau in the U.S. state of Texas. As of the 2010 census, its official population had reached 157,107. The county seat is San Marcos. The county is named for John Coffee Hays, a Texas Ranger and Mexican\u2013American War officer. Hays County is part of the Austin-Round Rock, TX Metropolitan Statistical Area.