I found your post while looking for my lost Robertsons. I also am in search for William Robertson. My line goes through Mitchell Robertson (b about 1805 d after 1880 GA) of SC. A gg uncle was born in Lancaster Co SC in 1839 George Chapman Robertson, my gggrandfather was his brother William Charles Robertson. They were sons of Mitchell and Abigail Walker Robertson. The only other info about this name is that William was the first of this line in SC "and through this line came Mitchell..." I don't know if Mitchell is Williams son or not. Do you know of any of these names?