Since it has a hole for a sling swivel, I'd say it from a military weapon.
Since it appears to be brass, I'd say it was made during the CW or pre-civil war. Post war military trigger guards that you would expect to find in Tn. would be made or steel/iron (example would be a 45-70 Trapdoor Springfield).
Several common foreign import muskets used in Tn. during the CW had brass trigger guards (e.g. Enfields and some of those "pumpkin slinger" German muskets).
Good find, tell us more about your hunt please.