| Name | Jefferson County |
| State | Illinois |
| FIPS Code | 17081 |
| County Seat | Mount Vernon |
| Timezone | Central Daylight Time (CDT) |
| Population (2024) | 36,331 |
| Population Growth Rate(2020-2024) | -2.15% |
| Majority Ethnicity | White 89.02% |
| Public School Majority Ethnicity | White 75% |
| Partisan Voting Index | Strongly Republican:+24 |
| Unemployment Rate (May 2026) | 6.0% |
| Sales Tax Rate (2025) | 9.5% |
| Area Code(s) | 618 |
| Race/Ethnicity | Percentage of Population (2023) |
|---|---|
| White | 89.02% |
| African American | 6.83% |
| Hispanic | 2.86% |
| Asian | 1.05% |
| Native American | 0.22% |
| Hawaiin/Pacific Islander | 0.02% |
| Race/Ethnicity | Percentage of Public School Students (2023) |
|---|---|
| White | 75.34% |
| African American | 12.38% |
| Hispanic | 3.23% |
| Asian | 0.71% |
| Native American | 0.06% |
| Hawaiin/Pacific Islander | 0.02% |