IllinoisAtlas.com

Provides freely available maps in PDF or JPEG format depicting a vast range of features. An ongoing project of the Data & Mapping Services Division of the Center for Governmental Studies at Northern Illinois University.
http://www.illinoisatlas.com/

Historical Maps of Illinois and the Northwest Territory

Joint project by University of Illinois and the Follet Corporation. Features numerous annotated images of geographical maps of Illinois, counties and cities along with the Midwest.
http://images.library.uiuc.edu/projects/historical_maps/

World Sites Atlas: Illinois Road and Hotel Map

A compact map showing interstate and U.S. highways plus major cities and towns.
http://www.sitesatlas.com/Maps/Maps/IL1.htm

IDOT State Road Map

Provides interactive maps of the state and can be searched by city, town or state park. Also, features printable map options, along with current and winter road conditions.
http://www.dot.state.il.us/maps.html