On what date did the Constitutional Convention sign the U.S. Constitution?

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

Delegates signed the completed document at the Pennsylvania State House in Philadelphia, the building now known as Independence Hall. Thirty-nine delegates signed, while several delegates who had participated in the convention declined to sign. George Washington, who had presided over the convention, signed first.

The convention had met from May 25 through September 17, 1787. Its original purpose was to revise the Articles of Confederation, but the delegates ultimately produced an entirely new framework for the federal government. The proposed Constitution then went to state ratifying conventions.

Signing did not make the Constitution immediately operative. Article Seven required nine states to ratify it, and New Hampshire reached that threshold in June 1788. The first Congress under the Constitution convened in March 1789, and the new government began its work that year.