High Quality Content by WIKIPEDIA articles! The Tualatin Valley is a farming and suburban region southwest of Portland, Oregon in the United States. The valley is formed by the meandering Tualatin River, a tributary of the Willamette River at the northwest corner of the Willamette Valley, east of the Northern Oregon Coast Range. Most of the valley is located within Washington County, separated from Portland by the Tualatin Mountains. Communities in the Tualatin Valley include Forest Grove, Cornelius, Hillsboro, Aloha, Beaverton, Sherwood, Tigard, and Tualatin.