On what date did the Constitutional Convention sign the United States Constitution?

The Constitutional Convention signed the United States Constitution on September 17, 1787.

Delegates met in Philadelphia during the convention that began in May 1787. Rather than simply revising the Articles of Confederation, they designed a new framework for a stronger federal government. Fifty-five delegates attended at least some sessions, and 39 delegates signed the completed Constitution.

The signing date is different from the ratification dates. The Constitution took effect after the required states approved it, with New Hampshire providing the ninth ratification on June 21, 1788. The new federal government began operating in 1789, and George Washington was inaugurated as president on April 30 of that year.

The Constitution is therefore connected to the 250th-anniversary story but is not the document being commemorated by America250. The 2026 milestone marks the Declaration of Independence’s adoption in 1776, eleven years before the Constitution was signed.