Thirty-nine delegates signed the United States Constitution on September 17, 1787.
The Constitutional Convention included 55 delegates at various points, but only 42 were present on the final signing day. Of those present, 39 signed the document. Three delegates—George Mason, Elbridge Gerry and Edmund Randolph—refused to sign.
The signers represented 12 states; Rhode Island did not send delegates to the convention. Several prominent delegates, including Thomas Jefferson and John Adams, were abroad and therefore were not convention participants.
The number 39 is sometimes confused with the total number of convention delegates or the number of states that had ratified the Constitution. The document still required state ratification, and the new federal government began only after the constitutional process moved forward in 1788 and 1789.