Duck Key, FL has a population of 716 and is the 17,329th largest city in the United States. The population density is 1,196 per sq mi which is 307% higher than the Florida average and 1220% higher than the national average. The median age in Duck Key is 59 which is approximately 43% higher than the Florida average of 42. In Duck Key, 58% of the population over 15 years of age are married, 78% speak English and 19% speak Spanish. 16% of Duck Key residents were born in Florida, 52% were born out of state, 15% were born outside of the United States and 18% were foreign born.