What a conundrum. If you want a battle between uniformed soldiers, which took place during Morgan's Raid, the northernmost battle is Salineville, Ohio.
If you want a bank robbery by 22 Confederates in civilian clothes, you get the St. Alban's Vt Raid where no uniformed soldiers of either side were present, and the only one killed was a St. Alban's resident who was a Southern sympathizer.