There is increasing DNA evidence that this Rebecca Stevenson, spouse of Alexander Robertson, is Rebecca Stephenson, daughter of parents Adam Stephenson (son of William Stephenson, of the South Branch of the Potomac River, Augusta County, VA) born 1736 & Rebecca. So far no documentation but it's possible she traveled with her sister, Sarah Stephenson Hair/Hare and her brother, James Stephenson to Ross County, Ohio, marrying there. The rest of the party traveled on and eventually settled in Wayne Township, Hamilton County, Indiana along with the Joseph and William Waddle/Woddell.
