williamson_county,_texas | largestcity | round_rock,_texas <tsp> austin,_texas | ispartof | williamson_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 
the largest city of williamson county. texas is round rock and austin is part of the county as well.williamson county texas is part of the austin-round rock-georgetown metropolitan area