1) In 1858, the Iowa State Agricultural Society was established. The organization was formed to promote the growth and improvement of agriculture in Iowa, which has a long history of being a major industry in the state.

2) On May 31, 1918, the deadliest tornado in Iowa history struck the town of Charles City. The tornado resulted in 13 deaths and over 400 injured. It also caused significant damage to the town's buildings and infrastructure.

3) In 1968, the city of Des Moines experienced severe racial tensions that culminated in riots on May 31. The riots lasted for several days, resulting in injuries and arrests. The events were a reflection of the larger civil rights movement taking place across the country at the time.

4) May 31, 1985, saw the official dedication of the Field of Dreams baseball field in Dyersville, Iowa. The field was built as a movie set for the film of the same name and has since become a popular tourist attraction and venue for amateur baseball games.

5) On May 31, 2008, the Iowa Supreme Court legalized same-sex marriage in the state. This landmark decision made Iowa the third state in the US to legalize same-sex marriage and helped pave the way for further progress in LGBTQ+ rights across the country.