Jefferson County, Illinois

Jefferson County
Jefferson County
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.jeffersoncountyillinois.com

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.