Of 21 counties in the Garden State, Mercer County ranks 16th by size (228 square miles). Mercer County is in Central New Jersey. The total value of about 1,000 acres of farms recently listed for sale in Mercer County, New Jersey, was almost $5 million. Browse all Mercer County farms for sale on the Land Network to find the farm, cattle operation, hobby farm or other farm property that's right for your future business or individual needs. The most common type of land for sale by combined acreage in Mercer County is residential property.