Seaford, DE has a population of 7,417 and is the 4,962nd largest city in the United States. The population density is 1,417 per sq mi which is 285% higher than the Delaware average and 1464% higher than the national average. The median age in Seaford is 39 which is approximately 2% lower than the Delaware average of 40. In Seaford, 53% of the population over 15 years of age are married, 85% speak English and 9% speak Spanish. 50% of Seaford residents were born in Delaware, 39% were born out of state, 1% were born outside of the United States and 10% were foreign born.