Washington, D.C., became the permanent capital of the United States in 1800.
The Residence Act of 1790 authorized a federal district along the Potomac River, and President George Washington selected the site. The federal government moved from Philadelphia to the new capital in 1800, during President John Adams's administration.
The district was named for George Washington, while the city was named for Christopher Columbus. Washington, D.C., is not a state; it is a federal district created to serve as the seat of the national government.
Philadelphia had been the temporary capital immediately before the move, and New York City had served as the first national capital under the Constitution. Those earlier roles are why the permanent capital is sometimes confused with the nation's first capital.