Illinois Postal History Society maintains a resources list for researchers studying Illinois postal history.

Major Bibliographic Resources

Illinois Postal Historian
Scans. photocopies and interlibrary loan of Illinois Postal Historian back-issues are offered as a fee-based service from:
American Philatelic Research Library (APRL)

Illinois Clubs
Chicago Philatelic Society

Collectors' Club of Chicago

Rockford Stamp Club

Champaign-Urbana Stamp Club

Illinois Dealers and Associations
Stamp King
Midwest Stamp Dealers Association

Midwest Postal History Societies

Wisconsin Postal History Society page at the Wisconsin Federation of Stamp Clubs

Missouri Postal History Society St. Louis and Area Philately

Peninsular State Philatelic Society