Gardiner's Island is a small island in the Town of East Hampton, New York, in Eastern Suffolk County. It is located in Gardiner's Bay between the two peninsulas at the east end of Long Island. It is 6 miles long, 3 miles wide and has 27 miles of coastline.
The island has been owned by the Gardiner family and their descendants since 1639 when Lion Gardiner purchased it from the Montaukett chief Wyandanch. It is one of the largest privately owned islands in the United States, and is slightly smaller than Naushon Island in Massachusetts, owned by the Forbes family.
Wikipedia https://en.wikipedia.org/wiki/Gardiners_Island
Coordinates 41°5'31.151" N -72°6'20.195" E
