Austin,_Texas | isPartOf | Hays_County,_Texas Hays_County,_Texas | countySeat | San_Marcos,_Texas Austin,_Texas | isPartOf | Williamson_County,_Texas Williamson_County,_Texas | largestCity | Round_Rock,_Texas
Austin, Texas is part of Williamson County, where Round Rock is the largest city. Austin, Texas, is part of Hays County, Texas, where San Marcos is the county seat.