Land for sale in Mercer County recently totaled nearly $35 million and 3,000 acres. Mercer County ranks 15th in the Mountain State for the total acreage of land currently advertised for sale. Of all farms and rural real estate for sale in Mercer County, Princeton had the most land for sale. Mercer County is the 28th biggest county (420 square miles) in West Virginia. It's located in the Southeast West Virginia region of the state.