Seaside Park, NJ has a population of 1,635 and is the 12,202nd largest city in the United States. The population density is 2,495 per sq mi which is 249379% higher than the New Jersey average and 2654% higher than the national average. The median age in Seaside Park is 59 which is approximately 49% higher than the New Jersey average of 40. In Seaside Park, 60% of the population over 15 years of age are married, 98% speak English and 1% speak Spanish. 73% of Seaside Park residents were born in New Jersey, 25% were born out of state, 1% were born outside of the United States and 1% were foreign born.