The population of Upper Milford Township was 6,889 at the 2000 census.
Southern Lehigh and northern Bucks counties have seen numerous boundary changes since colonial times. Initially the area was part of Milford township in Bucks county. In 1752 Northampton county was formed and Upper Milford was in Northampton County. In 1812 Lehigh county was formed from part of Northampton leading to the current structure of Upper Milford township in Lehigh county.