Illinois is a state in the Midwestern region of the United States. It has the fifth largest gross domestic product (GDP),

the sixth largest population, and the 25th largest land area of all U.S. states. Illinois has been noted as a microcosm of the entire United States. With Chicago in northeastern Illinois, small industrial cities and immense agricultural productivity in the north and center of the state, and natural resources such as 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 international ports via two main routes: from the Great Lakes, via the Saint Lawrence Seaway, to the Atlantic Ocean and from the Great Lakes to the Mississippi River, via the Illinois River, through the Illinois Waterway. The Mississippi River, the Ohio River, and the Wabash River form parts of the boundaries of Illinois. For decades, Chicago's 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, through the 1980s, in politics.

The capital of Illinois is Springfield, which is located in the central part of the state. Although today Illinois's largest population center is in its northeast, the state's European population grew first in the west as the French settled lands near the Mississippi River, when the region was known as Illinois Country and was part of New France. Following the American Revolutionary War, American settlers began arriving from Kentucky in the 1780s via the Ohio River, and the population grew from south to north. In 1818, Illinois achieved statehood. Following increased commercial activity in the Great Lakes after the construction of the Erie Canal, Chicago was incorporated in the 1830s on the banks of the Chicago River at one of the few natural harbors on the southern section of Lake Michigan. John Deere's invention of the self-scouring steel plow turned Illinois's rich prairie into some of the world's most productive and valuable farmland, attracting immigrant farmers from Germany and Sweden. The Illinois and Michigan Canal (1848) made transportation between the Great Lakes and the Mississippi River valley faster and cheaper, and new railroads carried immigrants to new homes in the country's west and shipped commodity crops to the nation's east. The state became a transportation hub for the nation.

By 1900, the growth of industrial jobs in the northern cities and coal mining in the central and southern areas attracted immigrants from Eastern and Southern Europe. Illinois was an important manufacturing center during both world wars. The Great Migration from the South established a large community of African Americans in the state, including Chicago, who founded the city's famous jazz and blues cultures. Chicago, the center of the Chicago Metropolitan Area, is now recognized as a global city. Chicagoland, Chicago's metropolitan area, encompasses about 65% of the state's population. The most populous metropolitan areas outside the Chicago area include, Metro East (of Greater St. Louis), Peoria and Rockford.

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 born and raised in the state. Today, Illinois honors Lincoln with its official state slogan Land of Lincoln, which has been displayed on its license plates since 1954. The state is the site of the Abraham Lincoln Presidential Library and Museum in Springfield and the future home of the Barack Obama Presidential Center in Chicago.