Snohomish County is a county located in the U.S. state of Washington. With a population of 827,957 as of the 2020 census, it is the third-most populous county in Washington, after nearby King and Pierce counties, and the 72nd-most populous in the United States. The county seat and largest city is Everett. The county forms part of the Seattle metropolitan area, which also includes King and Pierce counties to the south.