I'm about 99% sure that it is an Eastern garter (thamnophis sirtalis). The reason i know this, is that i am from northern MN, and i have one exactly the same, except way bigger, and i have caught countless numbers of the same ones. It might be T. s. parietalis, but i doubt it, cause i have a true T. s. parietalis, that i caught last summer and they aren't even supposed to be in the north eastern half of MN.