Thirty-nine delegates endorsed the United States Constitution at its signing on September 17, 1787.
The signing took place at Independence Hall in Philadelphia, the same building where the Declaration of Independence had been adopted eleven years earlier. The delegates had spent four months debating a new framework of government at the Constitutional Convention.
The 39 signers represented 12 states. Rhode Island declined to send delegates to the convention, so it was the only state absent from the signing process. George Washington, who presided over the convention, signed first, followed by the other delegates.
The Constitution was not put into effect simply by the signatures. It had to be ratified by conventions in the states. New Hampshire became the ninth state to ratify it on June 21, 1788, allowing the Constitution to take effect, and the new federal government began operating in 1789.