New Hampshire became the ninth state to ratify the United States Constitution.
Its ratifying convention approved the Constitution on June 21, 1788. Article VII specified that ratification by nine of the thirteen states would be sufficient to establish the Constitution among the states that ratified it.
Delaware was the first state to ratify, on December 7, 1787, while New Hampshire supplied the decisive ninth approval. Virginia and New York ratified soon afterward, before the new federal government began operating. North Carolina and Rhode Island joined later, meaning the Constitution took effect before all thirteen original states had ratified.
Rhode Island is a frequent wrong answer because it was the last of the original thirteen states to ratify, doing so in 1790. New Hampshire's role was different: it was the state whose approval reached the constitutional threshold established by Article VII.