1. On May 23, 1898, the Battle of Las Guasimas took place in Cuba during the Spanish-American War. South Dakota soldiers, including the 1st Battalion of the South Dakota Volunteer Infantry, were involved in the battle and two were killed in action.

2. On May 23, 1900, the South Dakota state legislature passed a law establishing the South Dakota School of Mines and Technology in Rapid City. The school was created to educate students in mining and engineering, and is still in operation today.

3. On May 23, 1934, outlaws Clyde Barrow and Bonnie Parker were killed in a police ambush outside of Gibsland, Louisiana. The duo had previously been in South Dakota, where they robbed a bank in Belle Fourche in 1933.

4. May 23, 1976, was the date of the last execution in South Dakota. Prisoner Elijah Page was put to death by lethal injection for his role in the murder of a fellow inmate at the South Dakota State Penitentiary.

5. On May 23, 2019, the South Dakota Board of Education Standards approved new social studies standards for K-12 schools. The standards aimed to provide a more comprehensive understanding of Native American history and culture, and to include more diverse perspectives in the study of U.S. history.