The United States Constitution was signed in Philadelphia on September 17, 1787.
Delegates met at the Pennsylvania State House, the building now known as Independence Hall. The Constitutional Convention began in May 1787 and met through the summer to replace the Articles of Confederation with a stronger federal framework. George Washington presided over the convention.
The final document was signed by 39 delegates representing 12 states. Rhode Island did not send delegates. The Constitution then went to state conventions for ratification rather than taking effect simply because the Philadelphia meeting had approved it.
Philadelphia had already been central to the independence movement. The Second Continental Congress had met there, and the Declaration of Independence had been adopted at the same Pennsylvania State House in 1776. The city therefore connects two major milestones commemorated during America250: the declaration of independence and the creation of the federal Constitution.