| | Williamson County | IL | 17199 | | Marion-Herrin, IL 32060 | Carbondale-Marion-Herrin,
IL 166 | Central | metro county (urban) | federal/state
government-dependent | https://maps.google.com/?q=WilliamsonCounty+IL |
| | Winnebago County | IL | 17201 | | Rockford, IL 40420 | Rockford-Freeport-Rochelle,
IL 466 | Central | metro county (urban) | manufacturing-dependent | https://maps.google.com/?q=WinnebagoCounty+IL |
| | Woodford County | IL | 17203 | | Peoria, IL 37900 | Peoria-Canton, IL 427 | Central | metro county (urban) | manufacturing-dependent | https://maps.google.com/?q=WoodfordCounty+IL |
| | Cook County | IL | 17031 | Chicago-Naperville-Schaumburg,
IL 16984 | Chicago-Naperville-Elgin,
IL-IN 16980 | Chicago-Naperville,
IL-IN-WI 176 | Central | metro county (urban) | nonspecialized | https://maps.google.com/?q=CookCounty+IL |
| | DuPage County | IL | 17043 | Chicago-Naperville-Schaumburg,
IL 16984 | Chicago-Naperville-Elgin,
IL-IN 16980 | Chicago-Naperville,
IL-IN-WI 176 | Central | metro county (urban) | nonspecialized | https://maps.google.com/?q=DuPageCounty+IL |
| | Grundy County | IL | 17063 | Chicago-Naperville-Schaumburg,
IL 16984 | Chicago-Naperville-Elgin,
IL-IN 16980 | Chicago-Naperville,
IL-IN-WI 176 | Outlying | metro county (urban) | nonspecialized | https://maps.google.com/?q=GrundyCounty+IL |
| | McHenry County | IL | 17111 | Chicago-Naperville-Schaumburg,
IL 16984 | Chicago-Naperville-Elgin,
IL-IN 16980 | Chicago-Naperville,
IL-IN-WI 176 | Central | metro county (urban) | nonspecialized | https://maps.google.com/?q=McHenryCounty+IL |
| | Will County | IL | 17197 | Chicago-Naperville-Schaumburg,
IL 16984 | Chicago-Naperville-Elgin,
IL-IN 16980 | Chicago-Naperville,
IL-IN-WI 176 | Central | metro county (urban) | nonspecialized | https://maps.google.com/?q=WillCounty+IL |
| | DeKalb County | IL | 17037 | Elgin, IL 20994 | Chicago-Naperville-Elgin,
IL-IN 16980 | Chicago-Naperville,
IL-IN-WI 176 | Outlying | metro county (urban) | federal/state
government-dependent | https://maps.google.com/?q=DeKalbCounty+IL |
| | Kane County | IL | 17089 | Elgin, IL 20994 | Chicago-Naperville-Elgin,
IL-IN 16980 | Chicago-Naperville,
IL-IN-WI 176 | Central | metro county (urban) | nonspecialized | https://maps.google.com/?q=KaneCounty+IL |