On what date was the United States Constitution signed, a founding milestone connected with America250?

The United States Constitution was signed on September 17, 1787.

Delegates signed the document at the Pennsylvania State House in Philadelphia, the building now known as Independence Hall. The Constitutional Convention had met there from May through September to replace the ineffective Articles of Confederation with a stronger federal framework.

George Washington presided over the convention, while James Madison became its leading intellectual architect and later wrote many of the Federalist Papers. Thirty-nine delegates signed the final document, though not every delegate who attended the convention approved it.

Signing did not immediately put the Constitution into effect. Article VII required ratification by nine states. New Hampshire became the decisive ninth state on June 21, 1788, and the new federal government began operating in 1789. The Constitution therefore predates the United States government under its current framework by nearly two years.