Richland County is a county located in the U.S. state of Illinois. According to the 2020 United States census, it had a population of 15,813. Its county seat is Olney.

Clay County is a county in the southeastern portion of the U.S. state of Illinois. As of the 2020 United States Census, the population was 13,288. Since 1842, its county seat has been Louisville, in the center of the county's area.