The first Sears retail store opened in Chicago.
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The first Mormon Pioneers left their homes in Nauvoo, Illinois, and began the long trek to the Salt Lake Valley.
An F5 max rating tornado smashed through Plainfield, Illinois, killing 29 people, injuring 353, and causing $165 million in damages.
The first telephone call was made between New York and Chicago.
The world's first self-sustaining nuclear chain reaction happened in Chicago Pile-1 at the University of Chicago. It was overseen by Enrico Fermi.
The world's most infamous clown, John Wayne Gacy, went on trial after he murdered 33 young men in Cook County, Illinois.
