- King County, located in Western Washington, covers some 2,100 square miles extending from the crest of the Cascade Range to Puget Sound, including Vashon Island. It is Washington’s most populous county and contains its largest city – Seattle. It is the commercial center of the Pacific Northwest with public and private enterprises including Boeing, Costco, Group Health Cooperative, Washington Mutual, Starbucks Coffee Co., Amazon.com, University of Washington, Microsoft, PACCAR Inc, Weyerhaeuser, Seattle City Light, and the Port of Seattle, which operates the nation’s eighth-largest port as well as Sea-Tac International Airport…