Illinois is a state in the United States but may also refer to:

University of Illinois at Urbana-Champaign, the largest campus in the University of Illinois system

Illinois State University in Normal, Illinois

Illinois (album), a 2005 music album by Sufjan Stevens

Illinois Country, a region of colonial America

Illinois River, a tributary of the Mississippi River in the state of Illinois

The Illinois, a proposed mile-high skyscraper building designed in 1956

Illinois College, a private liberal arts college located in Jacksonville, Illinois

Jean-Baptiste Illinois Jacquet, a jazz saxophone player

Illinois Watch Company, a former manufacturer of watches

Illiniwek or Illinois Confederation, a tribe of North America

Illinois Territory, an organized territory of the USA from 1809 to 1818

Illinois language, spoken by the Illiniwek

Illinois River (Oklahoma) in Arkansas and Oklahoma

"Illinois" (state song), the official song of the State of Illinois

Illinois River (Oregon)

USS Illinois, the name of several United States Navy ships

Illinois River (Colorado)