Multnomah County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the county's population was 815,428. Multnomah County is part of the Portland–Vancouver–Hillsboro, OR–WA metropolitan statistical area. Though smallest in area, Multnomah County is the state's most populous county. Its county seat, Portland, is the state's largest city.