A definitive source for Chicago history, including images of many important Chicago maps is the:
Encyclopedia of Chicago

For various Chicago map links, please visit:
Chicago in Maps

Links to our fellow map societies can be found at:
Map Societies around the World

Calendars of cartographic meetings and exhibitions are at:
Cartography Calendars

A general gateway to old maps (the history of cartography, map collecting, map collections, map images, and much more) can be found at:
Map History / History of Cartography: The Gateway to the Subject

Information about The History of Cartography Project, an important research, editorial, and publishing venture supported by the Chicago Map Society is located at:
The History of Cartography Project

Links to cartographic resources at The Newberry:
Hermon Dunlap Smith Center for the History of Cartography
Special Map Collections and Strengths

The Newberry Library Cartographic Catalog (2015) is an indexed catalog of 85,000 maps, atlases, and secondary reference sources available at the library. This document, which has not been published and will no longer be updated, is available for download as an Adobe Acrobat PDF document (17,400 pages in 136 KB). To receive a copy, please use this link to contact the Newberry Library Reference Department.

Other Map-Related Links:
A commercial site that includes a listing of map dealers worldwide as well as other items that might interest collectors:
MapRecord Publications