Jonesboro is a city in Union County, Illinois, United States. The population was 1,853 at the 2000 census. It is the county seat of Union County, and was the location of the third of the Lincoln-Douglas debates, on 15 Sept, 1858.
Jonesboro is located at 37°27′4″N 89°16′7″W / 37.45111°N 89.26861°W / 37.45111; -89.26861 (37.451126, -89.268566).
According to the United States Census Bureau, the city has a total area of 1.9 square miles (4.9 km²), all of it land.