Siesta Key, FL has a population of 5,782 and is the 5,891st largest city in the United States. The population density is 2,444 per sq mi which is 732% higher than the Florida average and 2598% higher than the national average. The median age in Siesta Key is 64 which is approximately 54% higher than the Florida average of 42. In Siesta Key, 78% of the population over 15 years of age are married, 91% speak English and 3% speak Spanish. 11% of Siesta Key residents were born in Florida, 74% were born out of state, 2% were born outside of the United States and 12% were foreign born.