| Code | Name | Region |
|---|---|---|
| US6CK | Clark | IL |
| USCL4 | Clark | MO |
| USNJC | Clark | NJ |
| USZCK | Clark | PA |
| US9CK | Clark | SD |
| USK8R | Clark | TX |
| USCAK | Clark Fork | ID |
| USKFQ | Clarkdale | AZ |
| USCWW | Clarkesville | GA |
| USCK8 | Clarklake | MI |
| UST5L | Clarkrange | TN |
| USKSQ | Clarks | NE |
| USCS9 | Clarks Hill | IN |
| USCLP | Clarks Point | AK |
| USCKU | Clarks Summit | PA |
| USCKJ | Clarksboro | NJ |
| USYKG | Clarksbourg | MD |
| US5CB | Clarksburg | CA |
| USCMQ | Claremont | CA |
| US9CL | Claremont | IL |
| USC2M | Claremont | MN |
| USCEO | Claremont | NC |
| USCNH | Claremont | NH |
| USCO3 | Claremont | VA |
| USLRE | Claremore | OK |
| USEJC | Clarence | IA |
| USAEC | Clarence | NY |
| USCA7 | Clarence | PA |
| USCC9 | Clarence Center | NY |
| USRNN | Clarendon | AR |
| USXCW | Clarendon | TX |
| USZDC | Clarendon Heights | PA |
| USCH4 | Clarendon Hill | IL |
| USVNH | Clarendon Hills | IL |
| USICL | Clarinda | IA |
| USC7L | Clarington | OH |
| USLRI | Clarion | IA |
| USQCO | Clarion | PA |
| USCTU | Citrus Heights | CA |
| USC34 | Citrus Springs | FL |
| USIS3 | City Island | NY |
| USCC5 | City Of Commerce | CA |
| USJID | City Of Industry | CA |
| USCQX | Clackamas | OR |
| USCF2 | Claflin | KS |
| USIBP | Claiborne | MD |
| USIMF | Clair Mel City | FL |
| US7CL | Claire City | SD |
| USCGN | Clairton | PA |
| USXMY | Clallam Bay | WA |