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. On April 20, 1907, the area was reincorporated as the City of Sea Isle City, based on the results of a referendum held on April 30, 1907.
As of the census of 2000, there were 2,835 people, 1,370 households, and 794 families residing in the city. The population density was 1,287.3 people per square mile (497.5/km²). There were 6,622 housing units at an average density of 1, 162.2/km² (3,006.9/sq mi). The racial makeup of the city was 97.88% White, 0.28% African American, 0.39% Native American, 0.35% Asian, 0.04% Pacific Islander, 0.07% from other races, and 0.99% from two or more races. Hispanic or Latino of any race were 1.06% of the population.
As of the 2000 census, 30.5% of Sea Isle City residents were of Irish ancestry, the 34th-highest percentage of any municipality in the United States, and sixth-highest in New Jersey, among all places with more than 1,000 residents identifying their ancestry.
There were 1,370 households out of which 15.5% had children under the age of 18 living with them, 48.2% were married couples living together, 6.9% had a female householder with no husband present, and 42.0% were non-families. 37.4% of all households were made up of individuals and 18.5% had someone living alone who was 65 years of age or older. The average household size was 2.07 and the average family size was 2.71.
In the city the population was spread out with 15.7% under the age of 18, 5.1% from 18 to 24, 20.8% from 25 to 44, 31.4% from 45 to 64, and 27.1% who were 65 years of age or older. The median age was 51 years. For every 100 females there were 91.4 males. For every 100 females age 18 and over, there were 89.6 males.
The median income for a household in the city was $45,708, and the median income for a family was $62,847. Males had a median income of $42,713 versus $31,375 for females. The per capita income for the city was $28,754. About 6.4% of families and 7.6% of the population were below the poverty line, including 13.7% of those under age 18 and 10.2% of those age 65 or over.
Sea Isle City is a beach town with most of its housing used for vacation rentals and second homes. It has a 1.5 mile beachfront promenade and several arcades, shops, restaurants and bars in the center of town. The epicenter of the town is 48th street.
Exit 17 on the Garden State Parkway provides access to Sea Isle City via Sea Isle Boulevard which becomes JFK Blvd.
Sea Isle City has a trolley service that runs down Landis Avenue during the summer months. New Jersey Transit offers the 315 inter-city bus route that runs through the town once a day and shuttles people to and from Philadelphia
There was a train service that ran the length of the island on Pleasure Avenue. The train was in use from the early 1900s until the mid 1930s when the tracks were removed and the streets were paved due to increase use of cars.