| Code | Name | Region |
|---|---|---|
| USKNE | Skaneateles | NY |
| USKAF | Skaneateles Falls | NY |
| USTKQ | Skiatook | OK |
| US7SK | Skidmore | MO |
| USSQM | Skillman | NJ |
| USSP3 | Skippack | PA |
| USSKP | Skippers | VA |
| USSOK | Skokie | IL |
| USSH5 | Skowhegan | ME |
| USKVQ | Skull Valley | AZ |
| USKUE | Skull Valley | UT |
| USSKW | Skwentna | AK |
| USS5K | Skykomish | WA |
| USUYZ | Skyland | NC |
| USSVK | Slate Hill | NY |
| USZTD | Slatedale | PA |
| USSI4 | Six Mile | SC |
| USSXM | Sixela | NM |
| USKSX | Sixes | OR |
| USIMC | Sims | NC |
| USSIO | Simsboro | LA |
| USSZU | Simsbury | CT |
| USSC7 | Sinclair | WY |
| USIGR | Singer | LA |
| USSIN | Singer Island | FL |
| USSKS | Sinking Spring | PA |
| US2SI | Sinton | TX |
| USSNT | Sioux Center | IA |
| USSUX | Sioux City | IA |
| USFSD | Sioux Falls | SD |
| USXAF | Sioux Rapids | IA |
| USIRE | Siren | WI |
| USSS2 | Sisseton | SD |
| USISV | Sissonville | WV |
| US8IS | Sister Bay | WI |
| USYER | Sisters | OR |
| USIST | Sistersville | WV |
| USSIT | Sitka | AK |
| USSKJ | Sitkinak Island | AK |
| USSIE | Silver Springs | FL |
| USS4S | Silver Springs | NV |
| USSVR | Silver Springs | NY |
| USITK | Silver Star | MT |
| USSI3 | Silverado | CA |
| USS4D | Silverdale | PA |
| USSIF | Silverdale | WA |
| USS5V | Silverstreet | SC |
| USSO5 | Silverthorne | CO |
| USIER | Silverton | CO |
| USVET | Silverton | OH |