Washington, D.C., became the permanent U.S. national capital in 1800.
The Residence Act of 1790 authorized a federal district along the Potomac River. President George Washington selected the general location, and the new district was named after him. The federal government moved from Philadelphia to the District of Columbia in 1800.
The capital’s earliest federal buildings included the Capitol and the President’s House, later called the White House. Construction continued for years, and the city developed gradually rather than appearing fully formed when the government moved.
Philadelphia had served as the national capital at several points, and New York City was the capital when the Constitution began operating in 1789. Those earlier capitals are why the question is sometimes confused. Washington, D.C., is the federal capital associated with the permanent seat of government in the national story leading to America250.