Thirty-nine delegates endorsed the final United States Constitution on September 17, 1787.
The signing took place at the Pennsylvania State House, now known as Independence Hall, at the final session of the Constitutional Convention. Fifty-five delegates attended the convention at some point, but not all approved the finished document.
The convention represented twelve states because Rhode Island declined to send delegates. The final signatures included those of George Washington, Benjamin Franklin, James Madison, and Alexander Hamilton. Some delegates left Philadelphia before the document was completed, while others refused to sign.
The number 39 is therefore different from several nearby figures often confused in trivia. The original thirteen colonies became states, 55 delegates attended at some stage, and 39 delegates signed. Ratification by the states occurred afterward and was a separate process.