Diamond Beach is an unincorporated community and census-designated place located within Lower Township in Cape May County, in the U.S. state of New Jersey. The CDP, and all of Cape May County, is part of the Ocean City metropolitan statistical area, and is part of the Philadelphia-Wilmington-Camden, PA-NJ-DE-MD combined statistical area, also k…Diamond Beach is an unincorporated community and census-designated place located within Lower Township in Cape May County, in the U.S. state of New Jersey. The CDP, and all of Cape May County, is part of the Ocean City metropolitan statistical area, and is part of the Philadelphia-Wilmington-Camden, PA-NJ-DE-MD combined statistical area, also known as the Delaware Valley or Philadelphia metropolitan area. As of the United States 2020 Census, the CDP's population was 203, an increase of 67 from the 2010 census count of 136.