Jefferson County | |
|---|---|
 Jefferson County Courthouse in Mount Vernon | |
 Location within the U.S. state of Illinois | |
 Illinois's location within the U.S. | |
| Coordinates: 38°18′N 88°55′W / 38.3°N 88.92°W | |
| Country |  United States |
| State |  Illinois |
| Founded | 1819 |
| Named for | Thomas Jefferson |
| Seat | Mount Vernon |
| Largest city | Mount Vernon |
| Area | |
| • Total | 584 sq mi (1,510 km2) |
| • Land | 571 sq mi (1,480 km2) |
| • Water | 13 sq mi (30 km2) 2.2% |
| Population (2020) | |
| • Total | 37,113 |
| • Estimate (2023) | 36,320  |
| • Density | 64/sq mi (25/km2) |
| Time zone | UTC−6 (Central) |
| • Summer (DST) | UTC−5 (CDT) |
| Congressional district | 12th |
| Website | www |
Jefferson County is a county located in the southern part of the U.S. state of Illinois. According to the 2020 census, it has a population of 37,113.[1] The county seat is Mount Vernon.[2] Jefferson County contains the Mount Vernon, Illinois micropolitan area. It is located in the southern portion known locally as "Little Egypt". The western border of the county adjoins the Greater St. Louis consolidated metropolitan statistical area, the Metro-East region, and the St. Louis commuter region and market and viewing area.
- ^ "State & County QuickFacts". United States Census Bureau. Archived from the original on June 6, 2011. Retrieved July 6, 2014.
- ^ "Find a County". National Association of Counties. Archived from the original on May 31, 2011. Retrieved June 7, 2011.