| Code | Name | Region |
|---|---|---|
| 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 |
| USSEE | Snellville | GA |
| USSNI | Snohomish | WA |
| USNQA | Snoqualmie | WA |
| USA3Q | Snoqualmie Pass | WA |
| USV8S | Snover | MI |
| USNSW | Snow Hill | MD |
| USXSW | Snow Hill | NC |
| USYWV | Snow Shoe | PA |
| US4SN | Snowbird | UT |
| USSFZ | Smithfield | RI |
| USFTU | Smithfield | UT |
| USSMT | Smithfield | VA |
| USZSM | Smiths | NC |
| USSDF | Smiths Creek | MI |
| USSK6 | Smiths Grove | KY |
| USJHG | Smithsburg | MD |
| UST9A | Smithton | MO |
| USTQQ | Smithton | MO |
| USITN | Smithton | PA |
| USSTY | Smithtown | NY |