where is plum island?
For other uses, see Plum Island. Plum Island is an island in the Town of Southold in Suffolk County, New York in the United States. The island is situated in Gardiners Bay, east of Orient Point, off the eastern end of the North Fork coast of Long Island. It is about 3 miles (4.8 km) long and 1-mile (1.6 km) wide at its widest point.