Seffner is a census-designated place in Hillsborough County, Florida, United States. The population was 7,579 at the 2010 census, up from 5,467 at the 2000 census. ZIP codes for the Seffner area are 33584 and 33583.Approximately 13 miles east of downtown Tampa, Seffner serves as a suburban haven for commuters. While still characterized by towering live oak trees, strawberry farms and lakes, this small town has been growing rapidly. Housing subdivisions now dot the once rural landscape.