Jefferson County on the map of Illinois as of 2026. Cities, roads, borders and directions in Jefferson County of Illinois.

Jefferson County is situated in the southern part of Illinois. This wonderful county was named after Thomas Jefferson (1743-1826), third President of the United States, second Vice President of the United States, Governor of Virginia. The area of Jefferson County is about 571 square miles. The county, created in 1819, is populated today by 37 thousand residents. Mount Vernon is the county seat of Jefferson County. This map shows the borders of Jefferson County as well as neighboring counties, including major highways and natural objecsts as of 2026. Zoom in or out of the map using the plus/minus panel. Move the center of this map by dragging it. Also check out the satellite map of Jefferson County.