Marion County is a county located in the U.S. state of Illinois. As of the most recent data available, the county has a population of approximately 41,691 people, with a population density of about 72.89 persons per square mile.
The county spans a total land area of 572.00 square miles (1,481.00 square kilometers). The administrative center and county seat is Salem, which often serves as a hub for local governance and services. The largest city within the county by population is Centralia.
Geographically, Marion County experiences varied elevations, with its highest point at Alma 630 ft and its lowest point at Salem 0 ft. The region operates in the UTC-6.