Deer Island Deer Island Thorofare was a busy waterway in the 19th century, with the granite quarries and the fishing industry being a booming business. The lighthouse was built in 1857 on the western side of the Thorofare to aid mariners near Stonington. The 25-foot brick tower was built and fitted with a fourth-order Fresnel lens, The house,bell tower,boathouse and oil house were all added later. The Fresnel lens was replaced in 1958 with a modern optic. The only building left standing is the lighthouse itself.