There seems to be a plausible claim that Susannah Royall (born about 1665), wife of John Ellis of Tuckahoe (born about 1661) was a second cousin of the grandfather of Thomas Jefferson, author of the Declaration of Independance. Both appear to be grand-children of Katherine Banks, who first married Joseph Royall, and later married Henry Isham. Jefferson's genealogy is very well known. Henry Isham's daughter Mary married William Randolph (b 1651). Their son, Isham Randolph, was father of Peter Jefferson and grandfather of Thomas Jefferson. Their is a Sons of American Rev. application that shows Katherine Banks and Joseph Royall's son was also named Joseph Royall. Although I don't have primary documents, other sources agree with this. What I am less sure of is whether Susannah was actually the daughter of the younger Joseph Royall. Both the dates and the geography seem right, and there do not appear to be other Royall's around that might be her father. It appears that the younger Joseph may have been the only son of Katherine Banks and the elder Joseph Royall.
Thomas Jefferson lived with his father Peter at Tuckahoe Plantation, after the death of Wm. Randolph in 1745 so Peter could act as guardian for William's son Thomas Randolf. I have also found in on the Virginia Historical Society website an image of a manuscript containing a signed order from Peter Jefferson to a Capt. Charles Ellis. Capt. Ellis was either the son or grandson of John Ellis b. 1661. Clearly, they were in the same area.
If anyone know of additional evidence about this relationship, please post a response to this board.