This is a Common Garter Snake (Thamnophis sirtalis) and completely harmless. Garters are the most widely distributed North American snake. They are not venomous, but will release a foul-smelling liquid if threatened. If you zoom in, you can see the characteristic black forked tip on the red tongue. This is a female I think, judging by her size. They give birth to between 12 and 40 live young at a time. Common Garter Snake populations include far more males than females, so during mating season, they form "mating balls", in which one or two females are completely swamped by ten or more males. 😳
