| Code | Name | Region |
|---|---|---|
| USIWT | Swiftwater | PA |
| USJWI | Swisher | IA |
| USSWI | Swissvale | PA |
| USS4W | Switz City | IN |
| USZSW | Switzer | WV |
| USZS2 | Swoope | VA |
| USDSK | Swords Creek | VA |
| USS3Y | Sycamore | AL |
| USYYC | Sycamore | GA |
| USSYC | Sycamore | IL |
| USZIS | Sycamore | OH |
| USYDY | Sydney | ND |
| USZJF | Sykesville | MD |
| USS6K | Sykesville | PA |
| USSYU | Sylacauga | AL |
| USSYY | Sylmar | CA |
| USSL6 | Sylva | NC |
| USYNL | Sylvan Lake | MI |
| USYNX | Sylvania | AL |
| USXMZ | Sylvania | GA |
| USAE5 | Swansea | MA |
| USSS5 | Swansea | SC |
| USSWQ | Swanton | OH |
| USSWA | Swanton | VT |
| USS3V | Swanville | MN |
| USSW5 | Swanzey | NH |
| USXWR | Swarthmore/philadelphia | PA |
| USSXZ | Swartz Creek | MI |
| USSW7 | Swatara | PA |
| USSDS | Swedesboro | NJ |
| USDXU | Sweeny | TX |
| USSWG | Sweet Grass | MT |
| USHOE | Sweet Home | OR |
| USSS9 | Sweet Springs | MO |
| USAAJ | Sweetwater | FL |
| USWW8 | Sweetwater | OK |
| USWWE | Sweetwater | TN |
| USSWW | Sweetwater | TX |
| USSWZ | Swepsonville | NC |
| USXSN | Swifton | AR |
| USZIJ | Sutherlin | VA |
| USSMS | Sutter | CA |
| USXXK | Sutter Creek | CA |
| USSXU | Sutton | AK |
| USTON | Sutton | MA |
| USS55 | Sutton | NE |
| US8UT | Sutton | NH |
| USVMY | Sutton | VT |
| USSUP | Sutton | WV |
| USZYY | Suttons Bay | MI |