- a member of a confederacy of North American Indians of Algonquian stock, formerly occupying Illinois and adjoining regions westward.
- the Algonquian language of the Illinois and Miami Indians.
- a state in the central United States: a part of the Midwest. 56,400 sq. mi. (146,075 sq. km). Capital: Springfield. Abbreviations: IL (for use with zip code), Ill.
- a river flowing southwest from northeastern Illinois to the Mississippi River: connected by a canal with Lake Michigan. 273 miles (440 km) long.
- a state of the N central US, in the Midwest: consists of level prairie crossed by the Illinois and Kaskaskia Rivers; mainly agricultural. Capital: Springfield. Pop: 12 653 544 (2003 est). Area: 144 858 sq km (55 930 sq miles)
- a river in Illinois, flowing SW to the Mississippi. Length: 439 km (273 miles)