| | Calhoun County | IA | 19025 | | | | | nonmetro county (rural) | farm-dependent | https://maps.google.com/?q=CalhounCounty+IA |
| | Carroll County | IA | 19027 | | Carroll, IA 16140 | | Central | nonmetro county (rural) | nonspecialized | https://maps.google.com/?q=CarrollCounty+IA |
| | Cass County | IA | 19029 | | | | | nonmetro county (rural) | nonspecialized | https://maps.google.com/?q=CassCounty+IA |
| | Cedar County | IA | 19031 | | | | | nonmetro county (rural) | nonspecialized | https://maps.google.com/?q=CedarCounty+IA |
| | Cerro Gordo County | IA | 19033 | | Mason City, IA 32380 | | Central | nonmetro county (rural) | nonspecialized | https://maps.google.com/?q=CerroGordoCounty+IA |
| | Cherokee County | IA | 19035 | | | | | nonmetro county (rural) | manufacturing-dependent | https://maps.google.com/?q=CherokeeCounty+IA |
| | Chickasaw County | IA | 19037 | | | | | nonmetro county (rural) | manufacturing-dependent | https://maps.google.com/?q=ChickasawCounty+IA |
| | Clarke County | IA | 19039 | | | | | nonmetro county (rural) | manufacturing-dependent | https://maps.google.com/?q=ClarkeCounty+IA |
| | Clay County | IA | 19041 | | Spencer, IA 43980 | Spencer-Spirit Lake, IA 517 | Central | nonmetro county (rural) | nonspecialized | https://maps.google.com/?q=ClayCounty+IA |
| | Clayton County | IA | 19043 | | | | | nonmetro county (rural) | nonspecialized | https://maps.google.com/?q=ClaytonCounty+IA |