Illinois (ⁱ/ˌɪlᵻˈnɔɪ/ IL-i-NOY) is a state in the midwestern region of the United States. 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.

Although today the state's largest population center is around Chicago in the northern part of the state, the state's European population grew first in the west, with French Canadians who settled along the Mississippi River, and gave the area the name, Illinois. After the American Revolutionary War established the United States, American settlers began arriving from Kentucky in the 1810s via the Ohio River, and the population grew from south to north. In 1818, Illinois achieved statehood. After construction of the Erie Canal increased traffic and trade through the Great Lakes, Chicago was founded in the 1830s on the banks of the Chicago River, at one of the few natural harbors on southern Lake Michigan.John Deere's invention of the self-scouring steel plow turned Illinois' rich prairie into some of the world's most productive and valuable farmlands, attracting immigrant farmers from Germany and Sweden. Railroads carried immigrants to new homes, as well as being used to ship their commodity crops out to markets.

Illinois is a state in the United States.

Illinois may also refer to:

Places

Schools

Ships

SS Illinois was an iron passenger-cargo steamship built by William Cramp & Sons in 1873. The last of a series of four Pennsylvania-class vessels, Illinois and her three sister ships—Pennsylvania, Ohio and Indiana—were the largest iron ships ever built in the United States at the time of their construction, and amongst the first to be fitted with compound steam engines. They were also the first ships to challenge British dominance of the transatlantic trade since the American Civil War.

Though soon outclassed by newer and larger vessels, Illinois was destined to enjoy a long and distinguished career, first as a transatlantic passenger liner and later as the U.S. Navy's auxiliary vessel USS Supply. In the 1870s, Illinois may have been the first ship to successfully transport a shipment of fresh meat from the United States to Europe, twenty years before the introduction of refrigeration. As USS Supply, the ship served in both the Spanish–American War and the First World War, and crew members may have been the first United States personnel to fire a hostile shot in the latter. Illinois was scrapped in 1928.