Hardin County is a county located in the U.S. state of Illinois. According to the 2020 census, it has a population of 3,649, making it the least populous county in Illinois. Its county seat is Elizabethtown. Hardin County is located in the part of the state known as Little Egypt. Hardin County was named for Hardin County, Kentucky, which was named in honor of Colonel John Hardin, an officer in the American Revolutionary War and the Northwest Indian War.

Pope County is the southeasternmost county in the U.S. state of Illinois. According to the 2020 census, it had a population of 3,763, making it the second-least populous county in Illinois. Its county seat is Golconda. The county was organized in 1816 from portions of Gallatin and Johnson counties and named after Nathaniel Pope, a politician and jurist from the Illinois Territory and State of Illinois.