Charles Johnston was born in Ohio on January 6, 1844, and died on January 18, 1917, per his death certificate. This document also mentions that he is a shoemaker, a common enough profession, but also unique enough for me to confidently track Charles through several censuses. Note, that on Charles' death certificate he is listed as a Johnston.
Other than his death certificate and several census records I didn't have much concrete information about Charles. His father's name, Exum, was unique and there was an Exum Johnston living in Logan County, Ohio at the same time as Charles, but I could find no definitive connection that made me comfortable enough to link them. A brick wall.
Recently, I came back to this line to see what I could track down. I decided to focus a little more on Exum Johnston, Charles' father. His unique first name should be easy enough to delineate him from other Johnstons in the area. But in searches for "Exum Johnston" I find nothing. The next step was to try various different spellings and Exum Johnson brings up a hit on the 1860 census, with 16-year-old son Charles. With this spelling success in hand I checked Google Books for Exum Johnson and found a hit: The Johnsons and Johnstons of Corrowaugh in Isle of Wight County, Virginia, Volume 1, by Eddis Johnson and Hugh Buckner Johnston. It was only in a preview view, but there was Exum Johnson with the same birth date as the Exum Johnson I found on the 1860 census. The book was not at my local research center, but I happened to be traveling through a town with a volume in their library and made a quick stop.
Low and behold, Charles Johnson, born on January 6, 1844, is listed in the volume as a son of Exum Johnson. The family line starts in America in Isle of Wight County, Virginia and then a portion of the family immigrates to Logan County, Ohio. The pieces fit...but why the two names? Throughout the documentation I have on Charles I have an equal amount for both names. His children and subsequent generations all use Johnston. I'm not sure what made Charles change his name. He came from Quaker roots, is it possible he changed his name to separate himself from that culture later in life? I will probably never know, but at least I have learned that trying various name spellings when searching for ancestors really does pay off. Thanks Charles Johnston, Johnson!