Fleming Island, FL has a population of 29,247 and is the 1,464th largest city in the United States. The population density is 1,847 per sq mi which is 529% higher than the Florida average and 1938% higher than the national average. The median age in Fleming Island is 43 which is approximately 2% higher than the Florida average of 42. In Fleming Island, 66% of the population over 15 years of age are married, 92% speak English and 4% speak Spanish. 34% of Fleming Island residents were born in Florida, 58% were born out of state, 2% were born outside of the United States and 6% were foreign born.