Millsboro, DE has a population of 4,121 and is the 7,310th largest city in the United States. The population density is 1,109 per sq mi which is 201% higher than the Delaware average and 1124% higher than the national average. The median age in Millsboro is 38 which is approximately 5% lower than the Delaware average of 40. In Millsboro, 54% of the population over 15 years of age are married, 89% speak English and 10% speak Spanish. 47% of Millsboro residents were born in Delaware, 44% were born out of state, 1% were born outside of the United States and 8% were foreign born.