Twenty-seventh Amendment to the United States Constitution
As of 2022, the Twenty-seventh amendment is the last amendment that has been added to the Constitution.  It took longer for the states to ratify this amendment than any other in history.  The 1st United States Congress sent the suggested amendment to the states for their approval on September 25, 1789.  It was not until May 7, 1992, that enough states ratified the amendment for it to be added to the Constitution.  The ratification process had taken 202 years, 7 months, and 12 days  the longest in United States history.