| Name | What | Region | Country | Lat | Long | Elev ft. | Pop est |
|---|---|---|---|---|---|---|---|
| Sidney | city | Montana | United States | 47.72 | -104.16 | 1961 | |
| Sieben | city | Montana | United States | 46.90 | -112.13 | 4189 | |
| Signal Butte (historical) | city | Montana | United States | 45.95 | -106.35 | 3349 | |
| Silesia | city | Montana | United States | 45.56 | -108.84 | 3395 | |
| Silver Bow | city | Montana | United States | 46.00 | -112.67 | 5367 | |
| Silver Bow (historical) | city | Montana | United States | 48.87 | -108.72 | 3349 | |
| Silver Bow Park | city | Montana | United States | 46.00 | -112.50 | 5869 | |
| Silver City | city | Montana | United States | 46.76 | -112.17 | 4366 | |
| Silver Gate | city | Montana | United States | 45.01 | -109.99 | 7595 | |
| Silver King (historical) | city | Montana | United States | 47.10 | -112.48 | 5869 | |
| Silver Lake (historical) | city | Montana | United States | 46.17 | -113.24 | 6709 | |
| Silver Star | city | Montana | United States | 45.69 | -112.28 | 4494 | |
| Simko Trailer Court | city | Montana | United States | 48.56 | -109.67 | 2509 | |
| Simms | city | Montana | United States | 47.49 | -111.93 | 3599 | |
| Simpkins Place | city | Montana | United States | 45.31 | -109.41 | 5029 | |
| Simpson | city | Montana | United States | 48.93 | -110.21 | 2798 | |
| Singleshot | city | Montana | United States | 48.25 | -113.48 | 4399 | |
| Sioux Crossing | city | Montana | United States | 45.87 | -110.24 | 5390 | |
| Sioux Pass | city | Montana | United States | 47.92 | -104.33 | 2509 | |
| Sipes | city | Montana | United States | 47.93 | -114.39 | 3733 | |
| Sipple | city | Montana | United States | 46.92 | -109.76 | 4189 | |
| Six Mile (historical) | city | Montana | United States | 47.03 | -114.35 | 3349 | |
| Sixmile Crossing | city | Montana | United States | 45.69 | -105.19 | 3349 | |
| Sixteen | city | Montana | United States | 46.22 | -111.00 | 5078 | |
| Siyeh Bend | city | Montana | United States | 48.70 | -113.67 | 6082 |