| Code | Name | Region |
|---|---|---|
| USTSQ | Sequin | TX |
| USKSS | Serena | IL |
| USSGB | Sergeant Bluff | IA |
| USKQ3 | Sesser | IL |
| USSV9 | Seven Fields | PA |
| USEVP | Seven Points | TX |
| USQ6Z | Seven Springs | NC |
| USKVV | Seven Valleys | PA |
| USSKI | Selkirk | NY |
| USSEU | Sellersburg | IN |
| USXVI | Sellersville | PA |
| USSES | Selma | AL |
| USSQZ | Selma | CA |
| USXZY | Selma | IN |
| USSQC | Selma | NC |
| USOSM | Selma | OR |
| USSQD | Selma | TX |
| USSQE | Selmer | TN |
| USEIY | Seminary | MS |
| USSE5 | Seminole | FL |
| USSXO | Seminole | NC |
| USZMD | Seminole | OK |
| USSOE | Seminole | TX |
| USEME | Semmes | AL |
| USNCZ | Semora | NC |
| USXAH | Senath | MO |
| USSEN | Senatobia | MS |
| USS7C | Seneca | IA |
| USS3D | Sedalia | CO |
| USDMO | Sedalia | MO |
| USSE4 | Sedan | KS |
| USS2Y | Sedley | VA |
| USSDX | Sedona | AZ |
| USSW2 | Sedro Woolley | WA |
| USSWK | Seekonk | MA |
| USSY4 | Seeley | CA |
| USEFF | Seffner | FL |
| USSQU | Seguin | TX |
| USO8K | Seiling | OK |
| USSEC | Seiple | PA |
| USEHW | Selah | WA |
| USWLK | Selawik | AK |
| USSEL | Selby | CA |
| USYVD | Selbyville | DE |
| USEXL | Selden | NY |
| USSOV | Seldovia | AK |
| USS66 | Seligman | AZ |
| USSEG | Selinsgrove | PA |
| USYSE | Seaside | OR |
| USSH2 | Seaside Heights | NJ |