Washington County, Oregon

Washington County, Oregon
Washington County Courthouse in Hillsboro
Seal
Location in the U.S. state of Oregon
Oregon's location in the U.S.
Founded	July 5, 1843
Seat	Hillsboro
Largest city	Hillsboro
Area
• Total	726 sq mi (1,880 km2)
• Land	724 sq mi (1,875 km2)
• Water	2.2 sq mi (6 km2), 0.3%
Population (est.)
• (2015)	574,326
• Density	731/sq mi (282/km²)
Congressional district	1st
Time zone	Pacific: UTC-8/-7
Website	www.co.washington.or.us

Washington County is one of 36 counties in the U.S. state of Oregon. As of the 2010 census, the population was 529,710, making it the state's second most populous county. The county seat and largest city is Hillsboro.

Washington County is part of the Portland-Vancouver-Hillsboro, OR-WA Metropolitan Statistical Area.

Cities in Washington County include Hillsboro, Beaverton, Tigard, and Forest Grove, the county's oldest city.

Originally named Twality when created in 1843, the territorial legislature renamed it for the first president of the United States, George Washington, 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).

The county's major roads include small sections of Interstate 5 and Interstate 205, the Sunset Highway, Oregon Route 217, Oregon Route 47, Oregon Route 10, Oregon Route 6, and Oregon Route 8. Public transportation is primarily operated by TriMet and includes buses, the Westside Express Service commuter rail, and MAX Light Rail. Other transportation includes air travel at the Hillsboro Airport, private airfields and heliports, and heavy rail cargo on rail lines.