Short answers, pulled from the story.
Illinois is known as the Land of Lincoln, having sent Abraham Lincoln, Ulysses S. Grant, and Barack Obama to the presidency while they were state residents. It is also the site of Cahokia, the largest pre-Columbian urban center north of the Valley of Mexico, and Chicago, which became the world's fastest-growing city by the late 19th century.
Illinois became the 21st U.S. state in 1818. Its capital was initially at Kaskaskia, moved to Vandalia in 1819, then to Springfield in 1837, where it has remained ever since.
As of the 2020 census, Illinois has a population of 12,812,508. Approximately 65% of residents live in the Chicago metropolitan area, which covers only 9% of the state's land area. Chicago itself, with 2,746,388 residents in 2020, is the third-most populous city in the United States.
Illinois was central to the nuclear age. In 1942, the University of Chicago conducted the first sustained nuclear chain reaction as part of the Manhattan Project. Argonne National Laboratory activated the first experimental nuclear power system in the U.S. in 1957, and Fermilab near Batavia opened a particle accelerator in 1967 that was the world's largest for over 40 years. Illinois now leads all states in nuclear power generation, with eleven plants operating.
In 2025, Illinois's gross state product was $1.201 trillion. Major industries include agriculture (the state ranks first or second in soybean production and second in corn production), manufacturing, financial services, and logistics. Illinois is home to over 32 Fortune 500 companies, including John Deere, McDonald's, United Airlines, and Walgreens.
Cahokia Mounds, near present-day Collinsville, Illinois, is a UNESCO World Heritage Site and the largest pre-Columbian structure north of the Valley of Mexico. Monks Mound, its centerpiece, stands 100 feet high and covers 13.8 acres. The civilization that built it vanished in the 15th century for unknown reasons.