Sunday Oct 9 - 1887
Priesthood meeting at 8 A.M
... I[t] was decided that this conference was too large, and that this should be called the Middle
Tenn[essee] Con[ference] and reach from the line of R.R. between Nashville & Murfreesboro on the West to the Jellico line on the East. Embracing the State from N. to S. and extending into K[entuck]y. The East Tenn[essee] Con[ference] Was to go E[ast] from the Jellico line R. R. and take in a part of N[orth] C[arolina] S. H. Head, Pres[ident].
Sadly, the boundaries described here are a little vague for determining the overall boundaries. But they probably made sense when considering where the missionaries were working at the time. At the very least, they were the portion of the boundaries them meant something to Willard Carroll.
The railroad from Nashville to Murfreesboro was a very short (red) line. The Jellico Line was also short though not quite as much (green). It ran from Jellico, Tenn on the state line to Knoxville. I have made an educated interpretation that the intent was the line continued along the railroads to the North of Nashville and the south of Murfreesboro and Knoxville (blue in each case). In practice, the border changed without recorded notice. By 1895, missionaries from Middle Tennessee were preaching several counties west of that rail line. In 1903, when Tennessee was split off into the East Central States Mission, the boundaries were moved to stay within state lines. Here is an example from 1910, after the lines had been redrawn.