1. On May 15, 1911, the Wisconsin State Capitol building, located in Madison, was dedicated. It took 11 years to construct and cost $7.25 million. The building features a 200-foot dome, which is the fifth largest dome in the world.

2. On May 15, 1954, Brown v. Board of Education, a landmark decision by the United States Supreme Court, was handed down. The case ruled that racial segregation in public schools was unconstitutional. The decision ultimately led to the integration of schools, including those in Wisconsin.

3. On May 15, 1967, the Milwaukee Bucks, a professional basketball team, was founded. The team has played in the NBA since 1968 and has won one championship in 1971. The team plays their home games at the Fiserv Forum in Milwaukee.

4. On May 15, 1972, Governor Patrick Lucey of Wisconsin declared a state of emergency due to flooding caused by heavy rains. The flooding caused over $250 million in damage and resulted in 16 deaths. It was one of the largest natural disasters in Wisconsin history.

5. On May 15, 2015, the USA Triathlon Collegiate Club National Championships were held in Madison, Wisconsin. The event drew over 1,200 participants from colleges and universities across the country. It was the first time the event was held in Wisconsin.