The Willamette Valley (/wɪˈlæmɪt/) is a 150-mile (240 km) long valley in Oregon, in the Pacific Northwest region of the United States. The Willamette River flows the entire length of the valley, and it is surrounded by mountains on three sides – the Cascade Range to the east, the Oregon Coast Range to the west, and the Calapooya Mountains to the south.
The valley may be loosely defined as the broad plain of the Willamette, bounded on the west by the Oregon Coast Range and on the east by the Cascade Range. It is bounded on the south by the Calapooya Mountains, which separate the headwaters of the Willamette from the Umpqua River valley about 25 miles (40 km) south of Hidden Valley. Interstate 5 runs the length of the valley, linking its major communities.
Because of differing cultural and political interests, the Portland metropolitan area and Tualatin River valley are often not included in the local use of the term. Additionally, the east slopes of the Coast Ranges and the west slopes of the Cascade Range from Oakridge to Detroit Lake can be considered part of the Willamette Valley in a cultural sense, despite being mountainous areas.
Cities in the valley include, from south to north, Cottage Grove, Eugene, Corvallis, Albany, Dallas, Salem, Keizer, McMinnville, Oregon City, Hillsboro, Portland, and St. Helens. Parts of the following counties, from south to north, lie within the valley: Douglas, Lane, Linn, Benton, Polk, Marion, Clackamas, Yamhill, Washington, Multnomah, and Columbia. Sometimes the area around Albany and Corvallis and surrounding Benton and Linn counties is referred to locally as the Mid-Valley. Marion, Polk, and other counties are sometimes included in the definition of the Mid-Valley.