Glen St. Mary, FL has a population of 566 and is the 18,787th largest city in the United States. The population density is 1,222 per sq mi which is 316% higher than the Florida average and 1249% higher than the national average. The median age in Glen St. Mary is 27 which is approximately 36% lower than the Florida average of 42. In Glen St. Mary, 51% of the population over 15 years of age are married, 99% speak English and 0% speak Spanish. 82% of Glen St. Mary residents were born in Florida, 17% were born out of state, 0% were born outside of the United States and 1% were foreign born.