tarrant_county,_texas | largestcity | fort_worth,_texas <tsp> texas | capital | austin,_texas <tsp> arlington,_texas | ispartof | tarrant_county,_texas <tsp> arlington,_texas | ispartof | texas <sep> tarrant county is located in the us state of texas as of 2020, it had a population of 2,110,640 it is texas' third-most populous county and the 15th-most populous in the united states its county seat is fort worth 
fort worth. the largest city in texas and arlington are both part of tarrant county. austin is the state capital.tarrant county texas texas is the third-most populous county in the united states