Mercer County is in Western Illinois. Of the 102 counties in the state, Mercer County is 44th in terms of its size (568 square miles). Recent Land Network data shows roughly 1,000 acres of residential land for sale in Illinois's Mercer County, which is valued at a combined $3 million. The average price of residential acreage for sale in Mercer County was $180,085. Browse all residential land and rural property for sale in Illinois to find residential land and properties that suit your lifestyle needs, from existing residential homes and estates to land ready for future residential-property development.