pierce_county,_washington | country | united_states <sep> pierce county is a county in the us state of washington as of the 2020 census, the population was 921,130, up from 795,225 in 2010, making it the second-most populous county in washington, behind king county, and the 60th-most populous in the united states the county seat and largest city is tacoma formed out of thurston county on december 22, 1852, by the legislature of oregon territory, it was named for us 
pierce county. washington is located within the united states.it is the second-most populous county in washington and the 60th-most populous in the united states