The Quincy–Hannibal, IL–MO Combined Statistical Area, as defined by the United States Census Bureau, is an area consisting of one county in Western Illinois and three counties in northeast Missouri, anchored by the cities of Quincy and Hannibal.

Adams County is the westernmost county in the U.S. state of Illinois. As of the 2020 census, the population was 65,737. Its county seat is Quincy. Adams County is part of the Quincy, IL–MO Micropolitan Statistical Area.