On what date did delegates sign the United States Constitution at the end of the 1787 convention?

Delegates signed the United States Constitution on September 17, 1787, at Independence Hall in Philadelphia.

The signing concluded the Constitutional Convention, which had debated a new federal government for nearly four months. Thirty-nine delegates endorsed the document, representing twelve states; Rhode Island had declined to send delegates to the convention.

Signing did not immediately make the Constitution operative across the country. Article Seven required ratification by conventions in nine states. New Hampshire supplied the decisive ninth ratification on June 21, 1788, allowing the new framework of government to take effect.

Another important date is March 4, 1789, when the Constitution's new government began operating. George Washington was inaugurated as the first president on April 30, 1789. Thus September 17 marks signing, not ratification or the start of the federal government.