1. Missouri's admission to the Union: May 17, 1820 was a significant date in Missouri's history because it was the day that Missouri was officially admitted as a state to the Union. There were debates about whether or not Missouri should be a slave state, and there were concerns about maintaining a balance between slave and free states.

2. Missouri's first state capitol: On May 17, 1821, only a year after Missouri's admission to the Union, the first Missouri State Capitol building in Jefferson City was completed. The building was designed by Stephen Hills and is now part of the Missouri State Capitol Historic Site.

3. Wild Bill Hickok's birth: May 17, 1837 is the birthday of famous Wild West gunslinger, James Butler "Wild Bill" Hickok. He was born in Troy Grove, Illinois, but he lived in several Missouri towns, including Kansas City and Springfield, throughout his life.

4. Harry S. Truman's Senate career: On May 17, 1942, Harry S. Truman, Missouri's future President, was sworn in as a U.S. Senator from Missouri. Truman would go on to serve in the Senate until 1945 when he became Vice President under Franklin D. Roosevelt.

5. Missouri's Tornado Outbreak: May 17, 1957 marked one of the most destructive tornado outbreaks in Missouri history, with 31 tornadoes touching down across the state in a single day. The tornadoes caused extensive damage and resulted in the deaths of 26 Missourians.