Which state was the last to ratify the United States Constitution?

Rhode Island was the last state to ratify the United States Constitution.

Rhode Island approved the Constitution on May 29, 1790, nearly three years after the Constitutional Convention signed it. The state had refused to send delegates to the convention and remained wary of a stronger federal government.

Opponents in Rhode Island objected to federal taxation, the proposed national structure, and restrictions on state-issued paper money. The state’s political leaders also feared that ratification would weaken local control. Several earlier conventions rejected or postponed the question.

Congress increased the pressure by considering a trade embargo against Rhode Island. The state ratified before that measure could become law, making it the thirteenth and final state needed for a fully unified constitutional system. The Constitution itself had already taken effect in 1789 after nine states ratified it.