The United States Constitution was signed on September 17, 1787, the founding document preceding America’s 250th anniversary.
Delegates signed the Constitution at the Pennsylvania State House in Philadelphia, now known as Independence Hall. The Constitutional Convention had met from May through September 1787 to revise the Articles of Confederation, but it ultimately produced an entirely new framework for the federal government.
Thirty-nine delegates signed the document on September 17. The Constitution then went to the states for ratification. Article VII required approval from nine states before it could establish the new government, and that threshold was reached when New Hampshire ratified on June 21, 1788.
The signing date is often confused with Constitution Day, which is observed on September 17, and with the date the document took effect. The federal government began operating under the Constitution on March 4, 1789.