There are no poisonous snakes native to Alaska. Hawaii and Maine come in a close second, because each only has one venomous snake and one possibly venomous variety, respectively.
Besides not having poisonous snakes, there aren't even any non-poisonous snakes that have been documented as living year-round in Alaska. However, non-harmful garter snakes have been seen in Alaska's southern tip, but believed to be only passing through in search of warmer temperatures. Alaskan residents can legally keep non-venomous reptiles as pets, so if one of those creatures were to escape from its enclosure, it could add to the state's very small snake population.