Seaford, NY has a population of 15,891 and is the 2,691st largest city in the United States. The population density is 6,089 per sq mi which is 1597% higher than the New York average and 6621% higher than the national average. The median age in Seaford is 42 which is approximately 11% higher than the New York average of 38. In Seaford, 65% of the population over 15 years of age are married, 92% speak English and 2% speak Spanish. 87% of Seaford residents were born in New York, 5% were born out of state, 1% were born outside of the United States and 7% were foreign born.