The United States Constitution was signed in Philadelphia in 1787. Delegates to the Constitutional Convention signed the document on September 17, 1787, at the Pennsylvania State House, now Independence Hall.
The convention met from May through September to replace the Articles of Confederation with a stronger federal framework. George Washington presided, and the finished Constitution established the structure of the federal government through its legislative, executive, and judicial branches.
Signing did not immediately put the Constitution into effect. It required ratification by the states, and New Hampshire became the crucial ninth state to ratify it on June 21, 1788. The new government began operating in 1789. The Constitution is therefore a later milestone in the national story commemorated by America250, not the document that declared independence in 1776.