I definitely don't have any firm answers for you about Martha, but I thought I might be able to answer a couple of your more general questions, and maybe pass on some "clues."
You will likely see in your research a large family of "Killoughs."For a long time, the Killough researchers thought us "Kellows" to be part of their clan, with simply misspelled names.It is true that you will find a few "Killow" and "Kellough" branches in that family due to some bad spellings and varied pronunciations.The Killough history is fairly well documented in Northern (Scot-Irish) Ireland and in the northeast US.They eventually spread south and west as well.
A few years back, I assumed my Kellows to be part of that bunch (as they said) until I dug further and found that I could very well-document my family of "Kellows" in TN, NC, and originating in MD as early as the 1690's.That's when I got this board started.It turned out that my "Kellow" line pre-dated the "Killough" line in America by several decades.You can read some of my other posts here for further details.I have found that when I see the spelling "Kellow" it usually is attached to this bunch or another group that arrived about a hundred years later and settled in Pennsylvania.One of the major hang-ups though is that on some rare occasions even these "Kellows" will appear as "Killough" or "Kellough" and if you're not sure which family you are working with, things can get mixed up quickly!To further complicate things, I sometimes find my southern Kellows as "Kello," "Killow," "Killo," and even "Kelo" and "Kellough" in official records.
Who knows?Maybe we all go back to the same place, but I have found that "very generally" the Kellows seem to be more of Scot origin and arrived earlier that the "Killough" family who passed through Ireland on the way and arrived a generation or so later.Add to that the few families of southern England "Cornish" Kellows, who came in a couple of groups even later - mid to late 1800's.And I almost forgot, there's at least one separate wealthy well-known family named "Kello" in southcentral VA in the mid and late 1700's.They apparently came directly from England as correspondences to family members in England and America have been documented by their researchers.
Of course I am generalizing quite a bit so I hope no one thinks me too out of line!
So, assuming your Martha to be a "Kellow" rather than a "Killough" there are several possible families for her.The vast majority of the Kellow family I have documented in MD around 1690, then in NC, then TN, had gone no further than that by the 1840's.I do have some decent evidence that some "stray" siblings of that group may have been in central Arkansas by the middle 1800's.Who knows?Maybe some of them were also in MO.There are several other "unaccounted for" siblings from TN in the early to mid 1800's.I have not been able to find them at all after the TN records.And, if you go all the way back to Maryland in about 1780, there is another known sibling I cannot account for.
The other main group of "true Kellows" was in Pennsylvania in the 1800's, but I doubt they would have ventured out to MO by 1840.Other members of that family here on the board might be able to answer that better.
I have also seen at least one stray Kellow record from out in Iowa I believe in the middle 1800's.I have never quite figured them out either.Is Washington County, MO more toward the bootheel or further north toward Iowa?Many (if not most) of the southern MO settlers came from Tennessee early on so that may be a clue.Do you have a census record for Martha that shows her state of birth?
I noticed you also listed "Kelloe and Kellae" in your message.Most of the folks I mentioned here never used those spellings, especially Kellae.There is a census record for a "Kelloe" in NC (maybe 1800 or 1810).I never did "place" him, but I figured he might be part of that VA "Kello" clan.
Let me know if any of that peaks your interest because I can probably dig into the files and find more details.Thanks for posting on the Kellow board.