Thirty-nine delegates signed the United States Constitution in 1787.
The signing took place on September 17 at the end of the Constitutional Convention in Philadelphia. The convention had involved 55 delegates at various points, but not all of them remained through the final session, and three delegates who were still present refused to sign.
The signers represented 12 states because Rhode Island declined to send delegates to the convention. George Washington, who presided over the convention, signed first. Benjamin Franklin, then 81 years old, was the oldest signer, while Jonathan Dayton of New Jersey was the youngest at 26.
The number 39 is often confused with the number of delegates who attended the convention or with the nine states required for ratification under Article VII. Those are different figures. The Constitution became operative after the required state ratifications, while the 39 signatures recorded the delegates who endorsed the completed document.