The United States Constitution was signed on September 17, 1787, at the Constitutional Convention in Philadelphia.
Delegates met at Independence Hall, then known as the Pennsylvania State House, to revise the Articles of Confederation. Instead, they produced an entirely new plan of government. The convention began in May and concluded when the document was endorsed on September 17.
Thirty-nine delegates signed the Constitution, representing 12 states. Rhode Island had declined to participate. George Washington presided over the convention, and the final document included the framework for the legislative, executive, and judicial branches of the federal government.
The signing date is not the same as the ratification date or the start of the new government. New Hampshire supplied the ninth state ratification on June 21, 1788. The Constitution became operative in 1789, with George Washington inaugurated as the first president on April 30 of that year.