| Code | Name | Region |
|---|---|---|
| USCSM | Clinton | OK |
| USCQ3 | Clinton | PA |
| USCLN | Clinton | SC |
| USCQT | Clinton | TN |
| USJCL | Clinton | UT |
| USCI9 | Clinton | WA |
| USCWZ | Clinton | WI |
| USCQJ | Clinton Township | NJ |
| USLNH | Clinton, Township Of | MI |
| USCFX | Clifton | TX |
| USUCF | Clifton | UT |
| USCF4 | Clifton | VA |
| USFTF | Clifton Forge | VA |
| USCFH | Clifton Heights | PA |
| USCFP | Clifton Park | NY |
| USCSS | Clifton Springs | NY |
| USCF3 | Clifton, Mesa | CO |
| USJMX | Climax | CO |
| USIMX | Climax | GA |
| USXRR | Climax | NC |
| USZQC | Clinchfield | GA |
| USVCL | Clint | TX |
| US7CN | Clinton | AL |
| USQLA | Clinton | AR |
| USCLB | Clinton | CT |
| USCWI | Clinton | IA |
| USICC | Clinton | IL |
| USCIX | Clinton | IN |
| USC4N | Clinton | LA |
| USVND | Cleveland | OK |
| USUAI | Cleveland | TN |
| USCAV | Cleveland | TX |
| USVZD | Cleveland | UT |
| USQVD | Cleveland | VA |
| USCVW | Cleveland | WI |
| USC4V | Cleveland Heights | OH |
| USVCS | Cleves | OH |
| USXDX | Clewiston | FL |
| USQFF | Clifford | KY |
| US7LI | Clifford | MI |
| US2TO | Clifford Township | PA |
| USACN | Cliffside | NC |
| USCSD | Cliffside Park | NJ |
| USCLF | Cliffwood | NJ |
| USCFT | Clifton | AZ |
| USCFU | Clifton | NJ |
| USTCF | Clifton | PA |
| USIFQ | Clifton | SC |
| USIFT | Clifton | TN |
| USCMO | Clemmons | NC |