| Code | Name | Region |
|---|---|---|
| USY9V | Clayville | RI |
| USLEU | Cle Elum | WA |
| USCXI | Clear | AK |
| USCB2 | Clear Brook | VA |
| USEAF | Clear Lake | IA |
| USCK7 | Clear Lake | MN |
| USDS3 | Clear Lake | SD |
| USLQA | Clear Lake | WI |
| USC4D | Claudville | VA |
| USCLK | Claverack | NY |
| USVXJ | Claves | OH |
| USZCS | Clawson | MI |
| USCXT | Claxton | GA |
| US8CY | Clay | AL |
| USUKY | Clay | KY |
| USCY6 | Clay | NY |
| USCYK | Clay Center | KS |
| USZCI | Clay Center | NE |
| USC9C | Clay Center | OH |
| US5CT | Clay City | IL |
| USCI8 | Clay City | KY |
| USCC6 | Claycomo | MO |
| USCLA | Claymont | DE |
| USCP2 | Claypool | AZ |
| USYPO | Claypool | IN |
| USQCB | Claysburg | PA |
| USCXQ | Clayton | AL |
| USCJX | Clayton | CA |
| USC9L | Clarksburg | MD |
| USCG4 | Clarksburg | NJ |
| USCLX | Clarksburg | TN |
| USCKB | Clarksburg | WV |
| USCKM | Clarksdale | MS |
| USCKS | Clarkston | GA |
| USLRT | Clarkston | MI |
| USCKL | Clarkston | WA |
| USCLV | Clarksville | AR |
| USCKQ | Clarksville | IN |
| USKVI | Clarksville | MD |
| USKIV | Clarksville | MI |
| USUA2 | Clarksville | MO |
| USC2K | Clarksville | OH |
| USCK6 | Clarksville | PA |
| USCKV | Clarksville | TN |
| USXEO | Clarksville | TX |
| USCVY | Clarksville | VA |
| USCJK | Clarkton | NC |
| USYCK | Clatskanie | OR |
| USCXE | Clarita | OK |
| USC24 | Clark | CO |