Land for sale in Mason County recently totaled approximately $5 million and nearly 1,000 acres. Mason County ranks 92nd out of 102 counties in Illinois for the total acreage of land currently advertised for sale. Among cities in Mason County with farms and rural real estate for sale, Forest City had the most land for sale. Mason County is the 47th biggest county (563 square miles) in Illinois. It's located in the Western Illinois region of the state.