There are 3 or 4 Buchanan family lines in Humphreys County that do not consider themselves related. When I recently asked an 80+ year old Buchanan relative about Charley Buchanan, owner of Buchanan Cooperage & Lumber in Johnsonville, TN around 1898-1899, he said "Oh, that line isn't related to us." So you can't rely on late 1800 census data to connect them all.
The line from Edmund Buchanan and his relatives (possibly James and John Bohanan) were all in District 4 in the early 1800s, which is the southwestern part of Humphreys County, now known as the Cuba Landing area, and northward to Roberts Creek, Sycamore Landing, a little later over to Bakerville area.