Chris, I have a Mary South in my family tree that may be the one you are searching.Don't have much on her other than her name, but the family info may help you to decide if this Mary South is the one you are looking for.
Mary South was daughter of Henry H. South and Hannah Walker.Henry H. was born 16 April 1811 in PA and died 22 February 1897 in Champaign Co. Hannah was born 12 May 1813 in PA and died 9 March 1892 in Champaign Co.Both are buried in Mt. Carmel Cemetary, Kinnard, OH.
Henry and Hannah had 6 children that I am aware of: 1. Elizabeth W. South born 1837 2. Henry C. (My GGrandfater) born 16 Sep 1841 and died 31 January 1933 3. Eliborn 1849 and died 1911 4. Mary (No Data) 5. Samuel (No Data) 6. Joseph (No Data)
Thus Mary could have been born from 1850 onward and if she was born as early as 1850, she would have been 67 in 1917 when I have a report of her living in Milford Center in Champaign County.Since she would have been 18 in 1868, it is possible that she could be Charles D. Chapman's mother.
Again, I don't know if this will help you, but if it fits, I have much more info on Henry C. South's family.