Offering a mix of rural-residential properties and recreational land for hunting and other uses, Sullivan County is located amidst New York's scenic Catskills Mountains.? Land for sale in Sullivan County recently totaled $310 million and approximately 100,000 acres. Sullivan County ranks fourth in the state for the total number of acres of land currently advertised for sale. Among cities in Sullivan County with land for sale, Monticello had the most land for sale. Based on its natural assets, tourism and recreation are important contributors to the Sullivan County economy. Sullivan County is the 23rd biggest county (996 square miles) in New York. It's located in the Southern New York region of the state.