If you knew who it was awarded TO, you might could make a nice price for yourself with a Civil War collector.
The Army of the Tennessee was quite notable and one of the best units of the entire Civil War.
A Union army in the West, named for the Tennessee River, under the command of 'little known' Maj. Gen. Ulysses S. Grant, along with 'other unknowns' William Tecumseh Sherman and James B. McPherson.
From the Battle of Fort Henry in 1862, to Sherman's March to the Sea.
The medal worth would be in who was it awarded to, which battles they fought in, how long were they in the Tennessee, and who was their commander, Grant, Sherman, McPherson?
This is where your value would be.
The Reunion itself was a group of reunions around the country at that time. I actually have a real photo of the reunion of the Army of Tennessee, the CONFEDERATE one, with my relatives in it.
It's an awesome photo but without knowing who the hell is who in it, the value isn't much.