| Code | Name | Region |
|---|---|---|
| US5CY | Clyde | NC |
| USC3Y | Clyde | NJ |
| USCYA | Clyde | NY |
| USCYB | Clyde | OH |
| USYDB | Clyde | TX |
| USLZA | Clyman | WI |
| USYME | Clymer | NY |
| USYYO | Clyo | GA |
| USCOC | Coachella | CA |
| USQCN | Coal Center | PA |
| USCOY | Coal City | IL |
| USYCO | Coal Run, Northumberland | PA |
| USCQ6 | Coal Township | PA |
| USZCV | Coal Valley | IL |
| USKL8 | Coaldale | PA |
| USZQZ | Coalfield | TN |
| USCG2 | Coalgate | OK |
| USCLG | Coalinga | CA |
| US5CO | Coalton | OH |
| USCLI | Clintonville | WI |
| USIOU | Clintwood | VA |
| USQL2 | Clio | MI |
| USQL3 | Clio | SC |
| USIVB | Clive | IA |
| USCQM | Cloquet | MN |
| USCXR | Closter/new Jersey | NJ |
| USXEP | Clover | ID |
| USCXV | Clover | SC |
| USXVR | Clover | WI |
| USOVX | Clover, Halifax | VA |
| USCYI | Cloverdale | CA |
| USKVD | Cloverdale | IN |
| USDCD | Cloverdale | OH |
| USCD8 | Cloverdale | OR |
| USCVV | Cloverdale | VA |
| USCVP | Cloverport | KY |
| USCVS | Clovis | CA |
| USCVN | Clovis | NM |
| USCU2 | Clute | TX |
| USCCN | Clinton | MA |
| USCNB | Clinton | MD |
| USQXZ | Clinton | ME |
| USCNC | Clinton | MI |
| USCT3 | Clinton | MN |
| USCBT | Clinton | MO |
| USCKC | Clinton | MS |
| USCTZ | Clinton | NC |
| USCNG | Clinton | NJ |
| USIKT | Clinton | NY |
| USCT9 | Clinton | OH |