1. On July 31, 1837, Chicago was officially incorporated as a city. Since then, it has grown to become the third-largest city in the United States, with a population of over 2.7 million people.

2. In 1893, the World's Columbian Exposition, also known as the Chicago World's Fair, officially closed on July 31. This historic event attracted over 27 million visitors and showcased some of the most innovative technology and culture of the time.

3. On July 31, 1908, the Cook County Forest Preserve District was established, which has since grown to become one of the largest forest preserve systems in the United States. Today, it spans over 70,000 acres and attracts millions of visitors each year.

4. In 1930, the famous "Highway Man" bandit, Arthur Barker, was shot and killed by FBI agents in Barrington, Illinois. Barker was a notorious criminal who was part of the notorious Barker-Karpis gang, and his death marked a significant victory for law enforcement.

5. On July 31, 1969, the Chicago Eight trial began in federal court. The trial was the result of protests and civil unrest surrounding the 1968 Democratic National Convention, and it famously included defendants such as anti-war activists Abbie Hoffman and Tom Hayden. The trial lasted for over five months and became a landmark case in the history of free speech and protest in the United States.