 According to the United States Census Bureau, the township has a total area of , of which, of it is land and of it (0.89%) is water.The area was first settled in 1789 when a road was built to connect Stockport on the Delaware River to the Susquehanna River at Cascade Creek.Harmony Township was formed in 1809 from parts of Willingborough (now Great Bend Twp) and New Milford Townships.