Land for sale in Boone County, Illinois, recently totaled $61 million and nearly 2,000 acres. Boone County ranks 15th out of 102 counties in Illinois for the combined amount of land currently advertised for sale. Of all locations in Boone County with farms and rural land for sale, Belvidere featured the most land for sale. Manufacturing and related services are the largest economic sectors in Boone County. Boone County is the 94th biggest county (282 square miles) in Illinois. It's located in the Northern Illinois region of Illinois.