It is the 5th most populous state and 25th largest state in terms of land area, and is often noted as a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal, timber, and petroleum in the south, Illinois has a diverse economic base and is a major transportation hub. The Port of Chicago connects the state to other global ports from the Great Lakes, via the Saint Lawrence Seaway, to the Atlantic Ocean; as well as the Great Lakes to the Mississippi River, via the Illinois River. For decades, O'Hare International Airport has been ranked as one of the world's busiest airports. Illinois has long had a reputation as a bellwether both in social and cultural terms and politics.

Three U.S. presidents have been elected while living in Illinois: Abraham Lincoln, Ulysses S. Grant, and Barack Obama. Additionally, Ronald Reagan, whose political career was based in California, was the only US President born and raised in Illinois. Today, Illinois honours Lincoln with its official state slogan, Land of Lincoln, which has been displayed on its license plates since 1954. The Abraham Lincoln Presidential Library and Museum is located in the state capital of Springfield.