The unincorporated village 'Middleford' was within Northwest Fork Hundred (a separate enumeration designation) in 1840 and in "Subdivision 11" in 1850.
The Post Office address 'Middleford' given in 1860 covered an area much larger than the little village; do not mistake the P. O. designation as showing people who actually lived in the village.
There can be many reasons for not finding people in 1840: people move, and may live in others' households.Females who were not heads of household were just not listed by name.
For 1850 also people may have moved, or might simply have been missed.Maybe not home when the enumerator came around (perhaps temporarily living with a married daughter, in which case the enumerator might have missed someone who went back home before the enumerator reached the daughter's house).
Some areas were just missed; I have personally found this to be the case with two different large ancestral families.