The Northwestern United States is a subportion of the Western U.S. region (which is, itself, even more ambiguous). In contrast, states included in the neighboring regions Southwestern U.S. and Great Plains are not simultaneously considered part of both regions.
Like the southwestern United States, the Northwest definition has moved westward over time. The 19th century Northwest (usually termed the "Old Northwest") comprised the Northwest Territory and gradually migrated across the Midwest to its current definition. The current area includes the old Oregon Territory (created in 1848–Oregon, Washington, Idaho, and areas in Montana west of the Continental Divide). The region is similar to Federal Region X, which comprises Oregon, Washington, Idaho, and Alaska.
It is home to over 13 million citizens.[dubious– discuss] Some of the fastest growing cities in this region and in the nation include Seattle, Bellevue, Tacoma, Vancouver, Kennewick, Pasco, Yakima, and Boise.
Together, these states have a combined population of 13,654,456. The largest cities and metropolitan areas in the Northwest are: