For America250, on what date was the U.S. Constitution signed?

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

Thirty-nine delegates endorsed the document at the Pennsylvania State House in Philadelphia, the building now known as Independence Hall. The Constitutional Convention had begun in May and continued for four months.

The signing did not immediately make the Constitution the operating framework of the United States. Ratification by nine states was required, and New Hampshire became the decisive ninth state on June 21, 1788.

September 17 is now observed in the United States as Constitution Day and Citizenship Day. The date is sometimes confused with July 4, 1776, which marks adoption of the Declaration of Independence, or March 4, 1789, when the new federal government began operating.