Awrkinsawwww. I'm not a native, having migrated from Texas.
The word is that killing a venomous snake that is posing a danger is prolly O.K. But technically, . . .
The last cottonmouth I killed was curled up in a laying box in our chicken house. Nasty critter!
I also found it remarkable that SQUIRRELS ARE A GAME ANIMAL in Awrkinsawwww, with a season and everything. In Texas, they were just considered vermin, but then maybe that's changed since I left.
My section of Illinois has no poisonous snakes. If I lived in any area that did, I would be packing every time I left the house. I don't have a thing about snakes, but I would not tolerate venomus types near my home.