Glenn --
Did you mean Cowan Tennessee? There's no listing for for a town named Cowen in Tennessee. Also, I don't understand how Sullivan County would be related with Cowan, if that's what you meant. These two places are in different parts of the state.
If you're asking about movements of the 19th Tennessee, Cowan makes good sense. On July 3, 1863, the Confederate Army of Tennessee was retreating through Cowan on the way towards Bridgeport, Ala., and Chattanooga.
If this soldier took the oath of allegiance, that information should be in his service file. Have you checked for a pension application?