It marks the west side of the mouth of the Norwalk River on northern Long Island Sound.

[2] In 1826 Gershom Smith, Sheffield's son in law, sold 4 of the island's 53 acres (21 ha) at the southwest point to the United States government for the purpose of building a lighthouse.

[1] The Fresnel lens from 1857 was moved into the new structure and with a focal plane 51 feet (16 m) above water it was visible for more than 12 miles (19 km).

[2] Sheffield Island Lighthouse was put up for sale in 1914 and purchased by Thorsten O. Stabell.

In the fall of that year, a great storm flooded the basement of the building and artifacts were lost or destroyed.