Hays County is a county located on the Edwards Plateau in the U.S. state of Texas. Hays County is part of the Austin-Round Rock, TX Metropolitan Statistical Area. As of the 2010 census, its official population had reached 157,107. The county seat is San Marcos. Hays, along with Comal and Kendall counties, was listed in 2017 as one of the nation’s ten fastest-growing large counties with a population of at least ten thousand. The county is named for John Coffee Hays, a Texas Ranger and Mexican–American War officer.