I checked the National Park Service's "Soldier & Sailors" site. One candidate might be Dennis Johnson that served with the 1st Squadron Georgia Cavalry (State Guards)(Gordon). There may be a Gordon County connection.

You might want to see his Compiled Service Records at the GA Archives in Morrow, or order them from the National Archives. Also, if he lived beyond 1890 he might have applied for a Confederate pension from the state he was residing in at the time.