Sea Isle City is a city in Cape May County, New Jersey, United States. It is part of the Ocean City Metropolitan Statistical Area. As of the 2010 United States Census, the city's population was 2,114, reflecting a decline of 721 from the 2,835 counted in the 2000 Census, which had in turn increased by 143 from the 2,692 counted in the 1990 Census. Visitors raise the population to as much as 40,000 during the peak summer season from Memorial Day to Labor Day. Sea Isle City is located on Ludlam Island, which also contains the Strathmere section of Upper Township.Sea Isle City was originally incorporated as a borough on May 22, 1882, from portions of Dennis Township, based on the results of a referendum held six days earlier. The borough was reincorporated on March 31, 1890. In March 1907, portions of Dennis Township and Upper Township were annexed to Sea Isle City. In April 1905, portions of Sea Isle City were annexed to Upper Township.