You know what? The Louvin Bros. made a mistake in the last couple of lines of the song and everybody since is singing it the mistaken way without bothering to examine the rhyming. They (and everyone else) sang:

They carried me down to Knoxville and locked me in A CELL.
My friends all tried to get me out, but none could go my bail.
I'm doomed to spend my life away down in this dirty old JAIL
Because I murdered that Knoxville girl, the girl I loved so well.

It should go, (and it rhymes):

They carried me down to Knoxville and put me in THE JAIL
My friends all tried to get me out, but none could go my bail.
I'm doomed to spend my life away down in this dirty old CELL
Because I murdered that Knoxville girl, the girl I loved so well.

See, it rhymes like this.

HTML line breaks added, typos corrected. --JoeClone, 12-Jun-02.