The United States Constitution became effective on June 21, 1788, when New Hampshire became the ninth state to ratify it.
Article VII required ratification by conventions in nine states before the Constitution could establish the new federal government among the states that approved it. New Hampshire’s vote supplied that ninth ratification, although the remaining states were still politically important and later joined the Union under the new system.
The Constitution had been signed in Philadelphia on September 17, 1787. Delaware was the first state to ratify, on December 7, 1787, while Rhode Island was the last of the original thirteen states, ratifying on May 29, 1790.
The new federal government began operations in 1789. George Washington was inaugurated as the first president on April 30, 1789, in New York City. The Constitution’s effective date is therefore earlier than the inauguration and different from the date the document was signed.