| Code | Name | Region |
|---|---|---|
| USJDG | Soldiers Grove | WI |
| USSXQ | Soldotna | AK |
| USZOL | Soledad | CA |
| USSOL | Solomon | AK |
| USSZO | Solomon | KS |
| USOMU | Solomons | MD |
| USSI5 | Solon | IA |
| USSO6 | Solon | ME |
| USSOO | Solon | OH |
| USOLG | Solvang | CA |
| USOVA | Solvay | NY |
| USL4W | Solway | MN |
| USSMV | Somerdale | NJ |
| USTSF | Somers | CT |
| USOFP | Somers | MT |
| USOJS | Somers | NY |
| USS5P | Somers Point | NJ |
| US6ST | Somerset | CA |
| USOMT | Somerset | CO |
| USSFL | Snowflake | AZ |
| USSM6 | Snowmass | CO |
| USSWM | Snowmass Village | CO |
| USSN5 | Snowshoe | WV |
| USSSN | Snyder | NE |
| USNYR | Snyder | NY |
| USNYD | Snyder | OK |
| USSNK | Snyder | TX |
| USSE3 | Soap Lake | WA |
| USOCR | Social Circle | GA |
| USSXS | Society Hill | SC |
| USONM | Socorro | NM |
| USXSR | Socorro | TX |
| USKQP | Soda Springs | CA |
| USYSS | Soda Springs | ID |
| US2SD | Soddy Daisy | TN |
| USXML | Soddy-daisy | TN |
| USSOB | Sodus | MI |
| USUYO | Sodus | NY |
| USSOD | Sodus Point | NY |
| USYSK | Smokey Point | WA |
| USO7T | Smoot | WV |
| USSDK | Smyrna | DE |
| USSMY | Smyrna | GA |
| USS7Y | Smyrna | NC |
| USNYY | Smyrna | NY |
| USMQY | Smyrna | TN |
| USSDD | Snead | AL |
| USQSD | Sneads | FL |
| USSKD | Sneads Ferry | NC |
| USSQY | Sneedville | TN |