Of 102 counties in the state, Mercer County ranks 44th in terms of size (568 square miles). Mercer County is in Western Illinois. Mercer County, Illinois, includes 1,000 acres of timberland for sale based on recent Land Network data. The combined market value of farmsand rural real estate for sale here was almost $200,000. Browse all Mercer County forest and timberland for sale on the Land Network to find the right timberland acreage for your commercial or individual investment needs. The most common type of land for sale by combined acreage in Mercer County is residential property.