Thirty-nine delegates signed the United States Constitution in 1787.
The signing occurred on September 17 at Independence Hall in Philadelphia, where the Constitutional Convention had met for four months. The delegates represented twelve states; Rhode Island declined to send delegates to the convention.
The number 39 refers specifically to the delegates who endorsed the completed document, not everyone who attended the convention. Fifty-five delegates attended at some point, and several refused to sign because they objected to parts of the final compromise. George Washington, the convention’s president, signed first.
The Constitution then went to the states for ratification rather than taking effect simply because it had been signed. It replaced the Articles of Confederation as the nation’s governing framework in 1789. Its signing forms a second major Philadelphia milestone alongside the Declaration adopted there in 1776.