What was the date of the final ratification of the constitution

May 29, 1790.

Explanation:

The drafting of the Constitution of the United States began on May 25, 1787, when the Constitutional Convention met for the first time with a quorum at the Pennsylvania State House (now Independence Hall) in Philadelphia, Pennsylvania to revise the Articles of Confederation, and ended on September 17, 1787, the day the Constitution drafted by the convention's delegates to replace the Articles was adopted and signed. The ratification process for the Constitution began that day, and ended when the final state, Rhode Island, ratified it on May 29, 1790.