| | | McLean County | IL | 17113 | | Bloomington, IL 14010 | Bloomington-Pontiac, IL 145 | Central | metro county (urban) | nonspecialized | https://maps.google.com/?q=McLeanCounty+IL |
| | | Macon County | IL | 17115 | | Decatur, IL 19500 | | Central | metro county (urban) | manufacturing-dependent | https://maps.google.com/?q=MaconCounty+IL |
| | | Macoupin County | IL | 17117 | | St. Louis, MO-IL 41180 | St. Louis-St.
Charles-Farmington, MO-IL 476 | Outlying | metro county (urban) | nonspecialized | https://maps.google.com/?q=MacoupinCounty+IL |
| | | Madison County | IL | 17119 | | St. Louis, MO-IL 41180 | St. Louis-St.
Charles-Farmington, MO-IL 476 | Central | metro county (urban) | nonspecialized | https://maps.google.com/?q=MadisonCounty+IL |
| | | Marshall County | IL | 17123 | | Peoria, IL 37900 | Peoria-Canton, IL 427 | Outlying | metro county (urban) | manufacturing-dependent | https://maps.google.com/?q=MarshallCounty+IL |
| | | Menard County | IL | 17129 | | Springfield, IL 44100 | Springfield-Jacksonville-Lincoln,
IL 522 | Outlying | metro county (urban) | farm-dependent | https://maps.google.com/?q=MenardCounty+IL |
| | | Mercer County | IL | 17131 | | Davenport-Moline-Rock
Island, IA-IL 19340 | Davenport-Moline, IA-IL 209 | Outlying | metro county (urban) | nonspecialized | https://maps.google.com/?q=MercerCounty+IL |
| | | Monroe County | IL | 17133 | | St. Louis, MO-IL 41180 | St. Louis-St.
Charles-Farmington, MO-IL 476 | Central | metro county (urban) | nonspecialized | https://maps.google.com/?q=MonroeCounty+IL |
| | | Peoria County | IL | 17143 | | Peoria, IL 37900 | Peoria-Canton, IL 427 | Central | metro county (urban) | nonspecialized | https://maps.google.com/?q=PeoriaCounty+IL |
| | | Piatt County | IL | 17147 | | Champaign-Urbana, IL 16580 | Champaign-Urbana-Denville,
IL 169 | Outlying | metro county (urban) | farm-dependent | https://maps.google.com/?q=PiattCounty+IL |
