Williamson_County,_Texas | largestCity | Round_Rock,_Texas Austin,_Texas | isPartOf | Williamson_County,_Texas Williamson_County,_Texas | countySeat | Georgetown,_Texas Austin,_Texas | isPartOf | Travis_County,_Texas
Round Rock is the largest city, and Georgetown is the county seat of Williamson County . Austin, Texas is part of this county as well as being located in Travis County.