Delegates signed the U.S. Constitution on September 17, 1787, a foundational milestone included in America250’s broader national story.
The signing occurred at the Pennsylvania State House in Philadelphia, the building now called Independence Hall. Thirty-nine delegates signed the completed document at the close of the Constitutional Convention. The convention had met from May through September to replace the weak Articles of Confederation with a stronger federal framework.
Signing did not immediately put the Constitution into operation. It required ratification by the states, and the document took effect after New Hampshire became the ninth state to ratify it on June 21, 1788. The new federal government began operating in 1789.
September 17 is now observed in the United States as Constitution Day and Citizenship Day. The date is sometimes confused with July 4, 1776, when the Declaration of Independence was adopted, or with March 4, 1789, when the constitutional government began.