Washington, D.C., formally the District of Columbia, is the capital of the United States, founded on July 16, 1790. The city is located on the bank of the Potomac River and is bordered by the states of Virginia and Maryland. The Washington metropolitan area, which includes the surrounding counties in Maryland and Virginia, is the ninth-largest in the United States with more than five million residents. When combined with Baltimore and its suburbs, the Baltimore-Washington metropolitan area has a population exceeding eight million residents, the fourth-largest in the country.