Land for sale in Illinois's Warren County recently totaled around $7 million and approximately 1,000 acres. Warren County ranks 57th out of 102 counties in Illinois for the total acreage of land currently advertised for sale. There were two properties listed as sold in Warren County through the Land Network Comparable Sales Program. This represented a total value of $551,000. Of all locations in Warren County with land for sale, Monmouth had the most land for sale. From an economic perspective, manufacturing and related services are the main sectors in Warren County. Warren County is Illinois's 49th largest county (543 square miles). It's located in the Western Illinois region of Illinois.