Thirty-nine delegates signed the United States Constitution at the Constitutional Convention in Philadelphia in 1787.
The signing occurred at Independence Hall on September 17, the convention’s final session. Delegates from 12 states were represented; Rhode Island declined to send delegates. Although 55 delegates attended at different points, only 39 endorsed the final document with their signatures.
Three delegates present at the convention refused to sign: George Mason, Elbridge Gerry, and Edmund Randolph. Several others had already departed. The Constitution then went to the states for ratification, with Article VII requiring approval from nine states. New Hampshire supplied the decisive ninth ratification on June 21, 1788, and the new federal government began operating in 1789.