The U.S. Constitution took effect in 1788 after New Hampshire became the ninth state to ratify it.
Article Seven required ratification by nine of the 13 states before the Constitution could take effect. Delaware was the first state to ratify, approving the document unanimously on December 7, 1787. Eight other states followed over the next several months.
New Hampshire ratified the Constitution on June 21, 1788, by a vote of 57 to 47. Its decision supplied the ninth approval required by Article Seven. Virginia ratified four days later, and New York followed in July.
The year 1788 is sometimes confused with 1787, when delegates signed the Constitution in Philadelphia, or with 1789, when the new federal government began operating. The final state of the original 13, Rhode Island, did not ratify until May 29, 1790.