|Washington County Oregon Cities/Towns - Aloha, Banks, Beaverton, Cornelius, Durham, Forest Grove, Gaston, Hillsboro (County Seat), King City, North Plains, Sherwood, Tigard, Tualatin
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Washington County is one of 36 counties in the U.S. state of Oregon. In 2000 census, its population was 445,342. The seat and largest city is Hillsboro.
Originally named Twality in 1843, the territorial legislature renamed it for the first president of the United States, George Washington, in 1849.