| Code | Name | Region |
|---|---|---|
| USQAC | Cato | NY |
| USCVM | Catonsville | MD |
| USXEL | Catoosa | OK |
| USACG | Catskill | NY |
| USTTT | Cattaraugus | NY |
| USC4L | Cavalier | ND |
| USVIY | Cave City | AR |
| USCCS | Cave City | KY |
| USC7A | Castle Rock | WA |
| USCJZ | Castleberry | AL |
| USCT5 | Castleton | VT |
| USCOH | Castleton On Hudson | NY |
| USDK6 | Castlewood | SD |
| USYCW | Castlewood | VA |
| USCL2 | Castorland | NY |
| USCVA | Castro Valley | CA |
| USCTV | Castroville | CA |
| USTVG | Castroville | TX |
| USQAX | Cat Spring | TX |
| US2CD | Cataldo | ID |
| USQTA | Catalina | AZ |
| USCKI | Catalina Island | CA |
| US8CT | Catarina | TX |
| USXEJ | Catasauqua | PA |
| USAOK | Catatonk | NY |
| USC47 | Cataula | GA |
| USUMO | Cataumet | MA |
| USCTQ | Catawba | NC |
| USCC3 | Cass City | MI |
| USCIB | Casselberry | FL |
| USRWX | Casselton | ND |
| USCZI | Cassopolis | MI |
| USTGW | Casstown | OH |
| USXSS | Cassville | MO |
| USQIC | Castaic | CA |
| USC7S | Castalia | NC |
| USAL8 | Castalia | OH |
| USC4P | Castanea | PA |
| USOMW | Castile | NY |
| USCAS | Castine | ME |
| USOK7 | Castle | OK |
| USCE6 | Castle Dale | UT |
| USCHY | Castle Hayne | NC |
| USC4H | Castle Hills | TX |
| USXSD | Castle Island | AK |
| USDP9 | Castle Pines | CO |
| USCSK | Castle Rock | CO |
| USLK9 | Castle Rock | MN |
| USKQE | Cascade | CO |
| USJDE | Cascade | IA |