Sea Isle City is a city in Cape May County, in the U.S. state of New Jersey. The city, and all of Cape May County, is part of the South Jersey region of the state and 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 2020 United States census, the city's year-round population was 2,104, a decrease of 10 (−0.5%) from the 2010 census count of 2,114, which in turn reflected a decline of 721 (−25.4%) from the 2,835 counted in the 2000 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.

Cape May County is the southernmost county in the U.S. state of New Jersey. Much of the county is located on the Cape May peninsula, bound by the Delaware Bay to its west and the Atlantic Ocean to its south and east. Adjacent to the Atlantic coastline are five barrier islands that have been built up as seaside resorts. A consistently popular summer destination with 30 miles (48 km) of beaches, Cape May County attracts vacationers from New Jersey and surrounding states, with the summer population exceeding 750,000. Tourism generates annual revenues of about $6.6 billion as of 2018, making it the county's single largest industry. The associated leisure and hospitality industries are Cape May's largest employers. Its county seat is the Cape May Court House section of Middle Township. The county is part of the Jersey Shore region of the state.