This is one of the only 5 square planned lighthouses in the country.

Derby Wharf Light Station has aided navigation in Salem Harbor since it was first lit in 1871. The Derby Wharf Light, along with the Hospital Point Light in Beverly, Massachusetts, and Fort Pickering Light Station on Winter Island in Salem, were designed to ‰ÛÏmark the main channel leading into this anchorage, with the view to its becoming a harbor of refuge which may be safely entered at any time,‰Û_ in the words of the 1870 report of the lighthouse board to the U.S. Treasury. The lighthouse is located on the end of Derby Wharf. Derby Wharf Light is about twelve feet square and about 20 feet high to the top of the cupola.