Land for sale in Sussex County recently totaled around $507 million and almost 9,000 acres. Based on the combined acreage of land and rural property for sale here, Sussex County has the most land for sale of all counties in the "Small Wonder. Lewes had the most land for sale. Sussex County is the largest county in Delaware (1,196 square miles, or some 100 percent of the state's total land area). It's located in the Southern Delaware region of the state.