San Marcos (de facto pronunciation /sæn ˈmɑrkəs/, less commonly /sæn ˈmɑrkoʊs/) is a city located in U.S. state of Texas, and is the Hays county seat. It is centrally located on the Interstate 35 corridor, between Austin and San Antonio.
Founded on the banks of the San Marcos River, it is considered by many archaeologists to be in the oldest continuously inhabited area in the Northern Hemisphere. San Marcos is home to Texas State University-San Marcos, and is the only known habitat for the endangered Texas Blind Salamander.
The population was 47,181 at the 2006 census. The Aquarena Springs ecological education center is located in San Marcos.[10]