Thirty-nine delegates signed the United States Constitution in Philadelphia on September 17, 1787.
The signatures were added at the end of the Constitutional Convention, held at the Pennsylvania State House, now known as Independence Hall. Fifty-five delegates participated in the convention at some point, but not all remained through the final day, and three participants refused to sign.
The signers represented twelve states; Rhode Island declined to send delegates to the convention. George Washington, the convention’s president, signed first. The document’s closing language recorded that the delegates endorsed it by the unanimous consent of the states present.
The number 39 refers specifically to delegates whose names appear as signers, not to every person who attended. Benjamin Franklin, aged 81, was the oldest signer, while Jonathan Dayton, aged 26, was the youngest. The Constitution then required ratification by the states before it could take effect.