It happened on the same day as the Chicago Fire. It covered several counties in Northern Wisconsin.
I spent some summers in Northern Wisconsin. There was one place I went where you could still burned out stumps. I assume that this was from the fire, and not something that happened later.
You should see the Kingston Plains up between Munising Mich and Grand Marias.
I dang near cry when I see that. All they had to do is NOT slash burn it and we could be logging great White Pine forests up there to this day.