The town is at the northeastern end of Long Island, New York on a peninsula called the North Fork and its extensions Plum Island, and Fishers Island. The Long Island Sound separates the town from Connecticut. The eastern end of the peninsula, near Orient Point, is north of the Town of Shelter Island, but the town is separated from the South Fork of Long Island by the Great Peconic Bay and the Little Peconic Bay. The western end of the town is the border of the Town of Riverhead. It is twenty-one miles from Orient Point to the border with Riverhead. Robins Island, a protected open space in Great Peconic Bay, is also part of the Town of Southold.
