That is a surprise. According the Wisconsin DNR website, there are not copper head snakes unless there is information off there and I checked multiple websites including one that has pictures of Wisconsin snakes. The only poisonous snakes in Wisconsin is the eastern massasauga and the Timber Rattlesnake.
dnr.wi.gov
I went by those sites since I like in south eastern Wisconsin in my entire life, but I'm not a woods person.
I didn't see snakes in the places I went to in Wisconsin such as the Dells, Door County, Shawano, New London, Suring, Gillett, and Green Bay.