I'm related to Margaret Blackman, but I am very interested in her though. At this point, I'm not entirely sure if Margaret was a widow of an unknown Mr. Blackman, or if she was a single mother, and Blackman was her surname.
Single mother seems more likely based on available evidence.
If she were a widow, instead of a single mother, I have no leads on who her husband might have been, nor do I know who her parents were. Unfortunately, this census was alphabetical, so we can't determine who her neighbors were, nor where she might have lived. That suggests she was married, or having children, already before 1820, but she was not listed on that census. There were several Blackman households in 1820 Marion that had a female her age and a small boy about the age of her apparent son. More research is needed to see if Margaret fits into any of those families.