On what date did delegates sign the U.S. Constitution at the 1787 Constitutional Convention?

Delegates signed the U.S. Constitution at the 1787 Constitutional Convention on September 17, 1787.

The signing took place in Philadelphia’s Pennsylvania State House, now Independence Hall, at the close of the convention. George Washington, who had presided over the meetings, signed first. Thirty-eight other delegates also signed, making 39 signatories in total.

Not every delegate supported the final document. Three delegates present—George Mason, Edmund Randolph, and Elbridge Gerry—refused to sign. Several other delegates had already left Philadelphia. Rhode Island had not participated in the convention at all.

The Constitution did not take effect immediately on the signing date. It required ratification by conventions in at least nine states. Delaware became the first state to ratify, while New Hampshire became the ninth on June 21, 1788, allowing the Constitution to become operative. The new federal government began work in 1789.

September 17 is now observed in the United States as Constitution Day and Citizenship Day. The date is a useful distinction from July 4, 1776, when Congress adopted the Declaration of Independence rather than the Constitution.