There was a total of nearly $6 million of farms and rural land for sale in Warren County recently on Land.com. The total size of all Warren County farms and rural land for sale was approximately 1,000 acres. Warren County ranks 54th in the Inland Empire for the total acreage of land currently advertised for sale. Of all farms, hunting land and other rural land and acreage for sale in Warren County, Monmouth had the most land for sale. Manufacturing and related services are the largest economic sectors in Warren County. Warren County is the 49th biggest county (543 square miles) in Illinois. It's located in the Western Illinois region of Illinois.