Washington County, Oregon

Washington County is one of the 36 counties in the U.S. state of Oregon. As of the 2010 United States Census, the population was 529,710,[1] making it the state’s second most populous county and most populous “Washington County” in the United States. The county seat and largest city is Hillsboro.[2][3]

Washington County is part of the Portland metropolitan area.

Cities in Washington County include Hillsboro, Beaverton, Tigard, Cornelius, Banks, Gaston, Sherwood, North Plains, and Forest Grove, the county’s oldest city.[4]

Originally named Twality when created in 1843, the territorial legislature renamed it for the nation’s first president in 1849. The original boundaries included the entire northwest corner of Oregon before sections became new counties. The Tualatin River and its drainage basin are almost entirely within the county, with the county nearly coterminous with the Tualatin Valley. It is bordered on the west and north by the Northern Oregon Coast Range, on the south by the Chehalem Mountains, and on the north and east by the Tualatin Mountains (or West Hills).