| Code | Name | Region |
|---|---|---|
| USSWN | Sewaren | NJ |
| USYSW | Sewell | NJ |
| USS5T | Sewell's Point | VA |
| USEWC | Sewickley | PA |
| USSZK | Seymour | CT |
| USEOU | Seymour | IA |
| USSER | Seymour | IN |
| USSEJ | Seymour | MO |
| USXMI | Seneca | IL |
| USEEC | Seneca | KS |
| USSNE | Seneca | MO |
| USUYP | Seneca | NY |
| USZYC | Seneca | PA |
| USSQW | Seneca | SC |
| USSFS | Seneca Falls | NY |
| USXMJ | Senecaville | OH |
| USSN2 | Senoia | GA |
| USSQF | Sepulveda | CA |
| USSQ5 | Sequatchie | TN |
| USSQV | Sequim | WA |
| 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 |