There are 68 US Post Offices in King County serving a total of 1,576,289 residents equating to 23,181 residents per post office. It's estimated that approximately 2,515,933 packages are handled across the 68 county post offices annually. King County is a county located in the U.S. state of Washington. As of the 2010 census its population was 1,931,249. King is the most populous county in Washington, and the 13th-most populous in the United States. The county seat is Seattle, which is the state's largest city. King County is included in the Seattle\u2013Tacoma\u2013Bellevue metropolitan statistical area. About two-thirds of the county's population lives in the city's suburbs. As of 2011, King County was the 86th highest-income county in the United States.