San Castle, FL has a population of 4,622 and is the 6,810th largest city in the United States. The population density is 11,081 per sq mi which is 3674% higher than the Florida average and 12131% higher than the national average. The median age in San Castle is 30 which is approximately 28% lower than the Florida average of 42. In San Castle, 52% of the population over 15 years of age are married, 45% speak English and 15% speak Spanish. 37% of San Castle residents were born in Florida, 14% were born out of state, 5% were born outside of the United States and 43% were foreign born.