You need to read all of Joseph Maddox information and search all census records.
I do not have documentation of this but this is what I believe to be true.
Sarah(sallie) A. Jackson, dau of James and Elizabeth in this cemetery, married, according to Maddox, John D. Rawlins.
If you will check the older dates on this family group, you will see that she,Sarah Jackson, married him and one of her daughters married a Duncan.
I have no primary info on this family. Perhaps someone else can help you more.I know they are closely related because of family members mentioning their names, etc. NO one ever thought to tell us younger ones why someone was called "cousin' because they were parts of their daily lives.
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