Indiana does not act like Illinois without Chicago. What I think we have to look at is that the state is at the center of a corn-heavy swath that votes heavily Republican. This region encompasses simply Southeastern Illinois, most of Indiana, and Western Ohio.
Southwestern Illinois votes much more like Missouri than Indiana. Northwest Illinois votes more like Iowa than Indiana. Illinois' downstate cities are also more liberal than Indiana's micro-cities.
What do you consider as Indiana's micro cities?
Fort Wayne, Anderson, Muncie, Terre Haute, Kokomo, Evansville, etc.
Compare voting patterns to Champaign, Springfield, Peoria, Bloomington (an exception), Rockford, Moline, etc.