The U.S. Constitution was ratified on June 21, 1788, when New Hampshire became the ninth state to approve it, making the Constitution the official framework of the U.S. government.

Quick Scoop

  • Key date: June 21, 1788.
  • Why that date matters: It was the day New Hampshire’s ratifying convention voted yes, giving the Constitution the required nine of thirteen states.
  • Draft vs. ratification: The Constitution was signed in Philadelphia on September 17, 1787, but it did not take effect until enough states ratified it the following year.
  • Final holdout: Rhode Island was the last of the original thirteen states to ratify, on May 29, 1790.

In everyday usage, when people ask “When was the U.S. Constitution ratified?” they almost always mean that pivotal moment on June 21, 1788, when ratification by the ninth state made it officially operative.

TL;DR: The U.S. Constitution was ratified on June 21, 1788, when New Hampshire became the crucial ninth state to approve it.

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