Jonesboro is a city in Union County, Illinois, United States. The population was 1,821 at the 2010 census, a decline from 1,853 in 2000. It is the county seat of Union County. The city is known for being tied to its close neighbor Anna, together known as Anna-Jonesboro.

Union County is a county located in the U.S. state of Illinois. According to the 2020 United States Census, it had a population of 17,244. Its county seat is Jonesboro. It is located in the southern portion of Illinois known locally as "Little Egypt".