Washington, D.C. formally the District of Columbia and commonly referred to as Washington, the District, or simply D.C., is the capital of the United States, founded on July 16, 1790. Article One of the United States Constitution provides for a federal district, distinct from the states, to serve as the permanent national capital. The City of Washington was originally a separate municipality within the federal territory until an act of Congress in 1871 established a single, unified municipal government for the whole District. It is for this reason that the city, while legally named the District of Columbia, is known as Washington, D.C.

The city shares its name with the U.S. state of Washington, which is located on the country's Pacific coast. The city is located on the north bank of the Potomac River and is bordered by the states of Virginia to the southwest and Maryland to the other sides. The District has a resident population of 599,657; because of commuters from the surrounding suburbs, its population rises to over one million during the workweek. The Washington Metropolitan Area, of which the District is a part, has a population of 5.4 million, the eighth-largest metropolitan area in the country.