The Cape Ann Light is located on Thacher Island and is southern of the two twin lighthouses that make up the Cape Ann Light Station. This light station was one to be established under colonial rule in and was also the first station in the US to mark a navigational hazard rather than a harbor entrance. The two lighthouses that stand today were built in 1861. The reason why two lighthouses were built is because prior to the invention of revolving lens system, flashes could only be produced by two lighthouses that alternated lights. The Cape Ann Light Station was was added to the National Register of Historic Places as Twin Lights Historic District – Cape Ann Light Station on October 7, 1971.