Founded in 1843, Sullivan County is one of 114 counties in the state of Missouri. Historically, Sullivan County was formed from Linn County. The city of Milan is the county seat. With FIPS code of 211, Sullivan County has a population of 5,934 and area of 651 square miles (1,686 km2).
List of all cities in Sullivan County, MO alphabetically
| City/Town | Postal Code | Area Code |
| Bairdtown, MO | 63556 | 660 |
| Boynton, MO | 63556 | 660 |
| Cora, MO | 63556 | 660 |
| Green Castle, MO | 63544 | 660 |
| Green City, MO | 63545 | 660 |
| Harris, MO | 64645 | 660 |
| Humphreys, MO | 64646 | 660 |
| Milan, MO | 63556 | 660 |
| Mystic, MO | 63545 | 660 |
| Newtown, MO | 64667 | 660 |
| North Salem, MO | 63566 | 660 |
| Owasco, MO | 63556 | 660 |
| Pennville, MO | 63545 | 660 |
| Pollock, MO | 63560 | 660 |
| Reger, MO | 63556 | 660 |
| Sidney, MO | 63544 | 660 |
| Sorrell, MO | 63556 | 660 |
| Winigan, MO | 63566 | 660 |