| Capital: | Mount Vernon |
|---|---|
| Origen y Formación del condado: | Edwards and White County |
| Población: | 38,827 habitantes |
| Área: | 571 sq mi |
| Localización del condado dentro de Illinois: |
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Localidades en Jefferson, Illinois
- Bald Hill Township Jefferson County
- Belle Rive
- Blissville Township Jefferson County
- Bluford
- Bonnie
- Casner Township Jefferson County
- Centralia
- Dix
- Dodds Township Jefferson County
- Elk Prairie Township Jefferson County
- Farrington Township Jefferson County
- Grand Prairie Township Jefferson County
- Ina
- McClellan Township Jefferson County
- Moore's Prairie Township Jefferson County
- Mount Vernon
- Mt. Vernon Township Jefferson County
- Nason
- Opdyke
- Pendleton Township Jefferson County
- Rome Township Jefferson County
- Scheller
- Spring Garden Township Jefferson County
- Texico
- Waltonville
- Webber Township Jefferson County
- Woodlawn Jefferson County