A total of nearly 1,000 acres were listed for sale in Mercer County recently, representing a total value of $8 million in Mercer County farms and rural land for sale. Mercer County ranks 96th out of 102 counties in the Land of Lincoln for the total number of acres of land currently advertised for sale. Of all farms and rural real estate for sale in Mercer County, New Boston featured the most land for sale. Mercer County is Illinois's 44th biggest county (568 square miles). It's located in the Western Illinois region of the state.