Philadelphia served as the United States capital from 1790 to 1800 while Washington, D.C., was being built.
The federal government moved from New York City to Philadelphia under the Residence Act of 1790. Philadelphia already had major political importance: the Continental Congress had met there, the Declaration of Independence had been adopted there, and the Constitutional Convention had convened there.
During the Philadelphia period, Congress met in Congress Hall and the president lived in the President's House. The arrangement was temporary because the federal government had agreed to establish a permanent capital along the Potomac River. Construction and planning proceeded during George Washington's presidency.
The capital moved to Washington, D.C., in 1800 after the White House and Capitol were ready for federal use. New York City had been the capital under the Constitution from 1789 until 1790, so Philadelphia was the second national capital under the new federal government.