I have also not found Isaiah Abernathy in MO, but there is an Isaiah who matches the birth date of 1792 in the 1830 and 1840 census of Licnoln Co. NC. One thing that puzzles me about the 1840 listing of Isaiah is that there isn't a female old enough to be Sally Low. In the 1860 census of Bollinger Co., MO, a Sarah Abernathy is listed in the household of Patrick Mccardell whose wife was Ama or Amy. Amy or Ama is usually listed as a daughter of Isaiah Abernathy, and this Sarah would fit the age of Sally Low. If this is Isaiah's wife, where was she in 1840?
I have found the Abernathys in Wayne and Bollinger County in the 1840 census, but I can't seem to figure out their relationships. Elijah had a daughter named Lucinda who married a John Abernathy. Do you think this could be the son of Isaiah?Do you known where Lawson Abernathy fits in? He is listed in Wayne Co, MO, in the 1840 census near Elijah.
Do you know the source for listing Isaiah as being born in 1792, and where does the list of children come from? If the 1840 census listing is the correct Isaiah, there could be as many as 12 children listed in that household, but only four are commonly listed in the internet postings.