Boise (less commonly known as Boise City) is a city located in the Northwestern United States in the state of Idaho. Boise is the capital and most populous city of the U.S. state of Idaho as well as the county seat of Ada County. Located on the Boise River, this is the principal city of the Boise City-Nampa metropolitan area and the largest city between Salt Lake City, Utah and Portland, Oregon. Boise passed Spokane in city population in 2001 census estimates and is now the third-largest in the northwest U.S. , behind Seattle and Portland. Boise serves as the primary government, economic, cultural, and transportation center for the area. As of the 2008 Census Bureau estimates, Boise's city population was 205,314 and Boise metropolitan area is estimated to have 599,753 inhabitants, by far the most populous metropolitan area in Idaho. It is also the 100th largest US city by population.