Duke Farms, located in Hillsborough, New Jersey, is the largest privately owned parcel of land in the state. The Duke family purchased the 2200 acre farmland at the turn of the century and spent about $10 million developing the landscape, creating lakes, hills and other topography.
Plans were made and begun for a large mansion on the property. A two level basement was built, but the house was never completed. You can still see evidence of the original foundation.
The farm can be visited for free and includes 18 miles of walking and biking paths. More information can be foundhere.