Founded in 1818, Jefferson County is one of 114 counties in the state of Missouri. Historically, Jefferson County was formed from St. Louis and Sainte Genevieve counties. The city of Hillsboro is the county seat. With FIPS code of 99, Jefferson County has a population of 227,771 and area of 657 square miles (1,702 km2).
List of all cities in Jefferson County, MO alphabetically
| City/Town | Postal Code | Area Code |
| Antonia, MO | 63052 | 636 |
| Arnold, MO | 63010 | 636 |
| Barnhart, MO | 63012 | 636 |
| Byrnes Mill, MO | 63049 | 636 |
| 63051 | 636 | |
| Cedar Hill, MO | 63016 | 636 |
| Crystal City, MO | 63019 | 636 |
| De Soto, MO | 63020 | 636 |
| Desoto, MO | 63020 | 636 |
| Dittmer, MO | 63023 | 636 |
| Festus, MO | 63028 | 636 |
| Fletcher, MO | 63030 | 573 |
| Hematite, MO | 63047 | 636 |
| Herculaneum, MO | 63048 | 636 |
| High Ridge, MO | 63049 | 636 |
| Hillsboro, MO | 63050 | 636 |
| Horine, MO | 63070 | 636 |
| House Springs, MO | 63049 | 636 |
| 63051 | 636 | |
| Imperial, MO | 63052 | 636 |
| 63053 | 636 | |
| Kimmswick, MO | 63053 | 636 |
| Lake Adelle, MO | 63016 | 636 |
| Liguori, MO | 63057 | 636 |
| Mapaville, MO | 63065 | 636 |
| Morse Mill, MO | 63066 | 636 |
| Olympian Village, MO | 63020 | 636 |
| Otto, MO | 63052 | 636 |
| Pevely, MO | 63070 | 636 |
| Sulphur Springs, MO | 63052 | 636 |
| Valles Mines, MO | 63020 | 636 |