Sebastian, FL has a population of 23,432 and is the 1,859th largest city in the United States. The population density is 1,725 per sq mi which is 487% higher than the Florida average and 1804% higher than the national average. The median age in Sebastian is 52 which is approximately 25% higher than the Florida average of 42. In Sebastian, 61% of the population over 15 years of age are married, 92% speak English and 4% speak Spanish. 28% of Sebastian residents were born in Florida, 64% were born out of state, 1% were born outside of the United States and 7% were foreign born.