| Code | Name | Region |
|---|---|---|
| US9AY | Callaway | VA |
| USCWG | Callaway Gardens | GA |
| USYYY | Callery | PA |
| USCA9 | Callicoon | NY |
| USL3E | Calpella | CA |
| USLMM | Calumet | MI |
| USCZ2 | Calumet | MN |
| USUET | Calumet | OK |
| USDWL | Caldwell | KS |
| USCDW | Caldwell | NJ |
| USCAQ | Caldwell | OH |
| USAWE | Caldwell | TX |
| USCDZ | Caledonia | MI |
| USEOI | Caledonia | MN |
| USC2Q | Caledonia | MS |
| USCO7 | Caledonia | NY |
| USCCD | Caledonia | OH |
| USCXX | Caledonia | WI |
| USCEB | Calera | AL |
| USCXL | Calexico | CA |
| USCLH | Calhan | CO |
| USCAH | Calhoun | GA |
| USC6H | Calhoun | IL |
| USCU3 | Calhoun | KY |
| USCU7 | Calhoun | TN |
| USCCI | Calhoun City | MS |
| USAHS | Calhoun Falls | SC |
| USQCJ | Califon | NJ |
| USKDE | Cade | LA |
| USCD5 | Cadet | MO |
| USCAD | Cadillac | MI |
| USJCZ | Cadiz | CA |
| USYCZ | Cadiz | KY |
| USQAZ | Cadiz | OH |
| USYYI | Cadiz | TX |
| USCM5 | Cadmus | MI |
| USCK5 | Cahokia | IL |
| USCJR | Cairo | GA |
| USCIR | Cairo | IL |
| US9CO | Cairo | MO |
| USQIR | Cairo | WV |
| USLBJ | Calabasas | CA |
| USLBQ | Calabash | NC |
| USCAL | Calais | ME |
| US7CI | Calais | VT |
| USCAU | Calcasieu | LA |
| USMI3 | Calcite | MI |
| USCDX | Caldwell | ID |
| USBY8 | Byron | GA |
| USXYB | Byron | IL |