williamson_county,_texas | largestcity | round_rock,_texas <tsp> austin,_texas | ispartof | williamson_county,_texas <tsp> williamson_county,_texas | countyseat | georgetown,_texas <tsp> austin,_texas | ispartof | travis_county,_texas <sep> williamson county (sometimes abbreviated as 'wilco') is a county in the us state of texas as of the 2020 census, its population was 609,017 its county seat is georgetown the county is named for robert mcalpin williamson (1804?–1859), a community leader and a veteran of the battle of san jacintowilliamson county is part of the austin-round rock-georgetown metropolitan statistical area 
austin is part of williamson county. texas and is located in travis county. georgetown is the county seat of williamson county. texas. where round rock is the largest city.williamson county texas is part of the austin-round rock-georgetown metropolitan area