Franktown is an unincorporated community and census-designated place (CDP) in Douglas County, Colorado, in the United States. The population was 395 at the 2010 census. The Franktown Post Office has the ZIP code 80116. Franktown is named for Hon. J. Frank Gardner, an early resident. Franktown was the first county seat of Douglas County, serving in this role from 1861 until 1863.