The timber species of these American pit vipers are found in 27 states
- Illinois DNR - Illinois.gov [PAR] Four species of Ililnois snakes, the copperhead (Agkistrodon contortrix), the 
cottonmouth ... Family Crotalidae - These are the venomous snakes including the 
... Illinois' venomous snakes are pit vipers, having a large opening, or "pit," on 
each side of ...