We have many maps of Illinois (mostly contemporary & government publications) but older maps (published before 1923) are also available from the following sites.
Illinois: Historical Maps Online
This collection contains images of maps charting the last 400 years of historical development in Illinois and the Northwest Territory. A collaborative effort between the University of Illinois Library, University of Illinois Press, and a selection of maps from the Newberry Library.
Federal Township Plats of Illinois (1804-1891)
At this site, the public can view a collection of 3,457 historical Illinois township plats that were hand-drawn between 1804-1891, each illustrated to show vegetation, geographical features, as well as man-made features. Hosted by the Illinois Digital Archives, Illinois State Library.
Digital Sanborn Maps for Illinois
Sanborn fire insurance maps for most cities and towns in Illinois for years between 1867 and 1970 are available from this database. Also, be sure to check our Sanborn Maps holdings on microfilm (but nothing in print available in the library.)
Library of Congress Map Collections -- Digitized Maps of Illinois
Map Collections of the Library of Congress include many maps of Illinois state & towns. Images are also available for downloading.
David Rumsey Collection - Illinois
Historical maps of Illinois (out of copyright, pre-1923 maps only) from the David Rumsey's wonderful collection. You can also download high resolution images!
Many historic maps of the Chicago area and the Great Lakes region.
IllinoisAtlas.com is an ongoing project of the Data & Mapping Services Division of the Regional Development Institute at Northern Illinois University.