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 is part of Williamson County (Texas), where the largest city is Round Rock. Austin is in Hays County, the county seat of which, is San Marcos Texas.