Seffner is an unincorporated census-designated place in Hillsborough County, Florida, United States. The population was 5,467 at the 2000 census, although its ZIP codes (33584 & 33583), which boundaries extend beyond the ones given by the census and include the places of Mango and a portion of Thonotosassa, have a population of around 35,000. Approximately 15 miles east of downtown Tampa, Seffner serves as a suburban haven for commuters. Characterized by towering live oak trees, strawberry farms and pristine lakes, this small town has been growing rapidly. Upscale, gated subdivisions now dot the once rural landscape.