1. In 1792, the Kentucky State Legislature enacted the first constitution adopting Kentucky as a state. This constitution was signed into law by Governor Isaac Shelby on May 21, 1792, and set the foundation for Kentucky governance.

2. In 1937, the Flood of '37 caused the Ohio River to rise over its banks and flood numerous communities in Kentucky. On May 21 of that year, the river reached its highest point at Louisville, Kentucky, where the water level reached 57.1 feet. This marked the highest level the Ohio River has ever reached in Louisville's history.

3. In 1956, Mammoth Cave National Park was established as a federally protected area in Kentucky. The park encompasses the world's longest known cave system and features diverse wildlife, underground rivers, and unique geological formations. On May 21, 1956, President Dwight D. Eisenhower signed legislation establishing the park.

4, In 1992, Kentucky's first African-American woman, Mae Street Kidd, was posthumously inducted into the Kentucky Women Remembered exhibit at the State Capitol in Frankfort, Kentucky. Kidd was a trailblazer for civil rights and community development in Kentucky and her impact is still celebrated today.

5. In 2008, the National Corvette Museum in Bowling Green, Kentucky, was struck by a massive sinkhole that swallowed eight rare Corvettes on display. The sinkhole, which measured 40 feet across and 60 feet deep, generated international attention and made headlines around the world. The incident occurred on February 12, 2014, but the museum began the process of removing the cars on May 21, 2014.