Various genealogies have our Thomas in a line of descent from either Thomas and Eigness Shannon of Pennsylvania or Nathaniel Shannon of Massachusetts. Both of these families were late 17th or early 18th settlers, and appear in colonial records at least a generation or two before the first confirmable documentation for our Thomas being here in 1767. Both families are associated with the Presbyterian church and both have extensive well documented genealogies which show them well integrated into the Scots-Irish communities in the various colonies.
Thomas/Eigness had a son named Thomas born about 1735. But he died in 1772 in Virginia, leaving a will that included no children and listed other relatives also mentioned in the will of his father Thomas. He mentions ‘cousins’ named Thomas in his will, but is probably referring to nephews. The other Thomas’ in both families are all accounted for and none are recorded as settling in Georgia.
In addition to the lack of any documentation, modern descendants from all three of these families have different yDNA that have no paternal genetic relationship in more than 5000 years. They are clearly unrelated genetic lineages in the modern era. It does not appear that this is the result of adoptions or illegitimacy between these families. In each case, the genetic association with their surnames is quite ancient. Our Shannon lineage simply does not descend from these other lines and has no older yDNA ancestry in North America so far confirmed.
On the other hand, Roger Casey seems to have had contact with members of the Thomas/Eigness lineage as well as with our Thomas/Eleanor line. So, there is a suggestion for some kind of potential relationship between them. It would not be impossible that these lines were coming out of a common population and were possibly related in some non-paternal way.
Bad Genealogy Rant: Thomas Shannon (1730-1794) and descendants. 