1. The Illinois State Capitol was dedicated on May 15, 1888. Designed by architects Cochrane and Garnsey, the Capitol building is an iconic landmark in Springfield, Illinois, and houses the offices of the governor, lieutenant governor, and other state officials.

2. On May 15, 1918, the deadliest train wreck in Illinois history occurred in Nashville, Illinois. A troop train carrying U.S. soldiers collided with a freight train, resulting in the deaths of 86 people and the injury of over 170 others.

3. May 15, 1932, marked the opening of the Chicago World's Fair, officially known as "A Century of Progress International Exposition." The fair showcased technological innovations and cultural exhibits, and attracted over 39 million visitors during its two-year run.

4. In 1946, May 15 was designated as "Peace Officers Memorial Day" in Illinois, honoring law enforcement officers who have died in the line of duty. The day is marked with ceremonies and tributes throughout the state.

5. On May 15, 1963, Dr. Martin Luther King Jr. visited Galesburg, Illinois, to deliver a speech at Knox College. The speech, titled "The Future of Integration," discussed the progress and challenges of the civil rights movement, and is considered one of King's most important speeches.