The Burger King in the town of Mattoon actually opened before the national chain and registered a statewide trademark in 1959. They sued to be able to operate as the only Burger King in Illinois, but were foiled in court -- though the Burger King chain is still not allowed to operate within 20 miles of the original restaurant.
The first Aquarium opened in Chicago, 1893.
The world's first Skyscraper was built in Chicago, 1885.
Metropolis the home of Superman really exists in Southern Illinois.