April 19, 1939
Connecticut ratifies the Bill of Rights
The first ten Amendments (Congress had passed 12), collectively known as the Bill of Rights, were proposed on September 25, 1789. They became effective after the 11th state, Virginia, ratified them on December 15, 1791.
Massachusetts, Georgia, and Connecticut didn't formally ratify them until 1939. Connecticut was the last to do so on April 19, 1939