Disappearing Ancestors in Census Records
You have found your ancestor in the 1820 and 1830 censuses, but he
cannot be located in the 1840 census. What can you do? There are
several approaches, but one idea is to locate his 1820 and 1830
neighbors in the 1840 census and see if your ancestor is nearby with
his name woefully misspelled or written in a barely legible fashion.
It is possible that your ancestor moved out of state; locating those
1820 and 1830 neighbors in that "new" location may allow you to find
your ancestor living there among them.
Of course, it is always possible that your ancestor is dead in 1840
and not enumerated at all. And there is always the chance that if he
is living with one of his grown children in 1840 that the grown child
is listed as the head of the household. In this case, the ancestor is
there, but just one of the "tic" marks for an older family member.