Seffner, FL has a population of 7,861 and is the 4,763rd largest city in the United States. The population density is 2,179 per sq mi which is 642% higher than the Florida average and 2306% higher than the national average. The median age in Seffner is 39 which is approximately 7% lower than the Florida average of 42. In Seffner, 53% of the population over 15 years of age are married, 79% speak English and 12% speak Spanish. 52% of Seffner residents were born in Florida, 33% were born out of state, 4% were born outside of the United States and 10% were foreign born.