The lateral stripe on the common gartersnake (Thamnophis sirtalis) may involve the upper half of
scale row 1 and always involves rows 2 and 3. The lateral stripe is of varying widths and shades of
yellow.

Here is a nearby wisconsin guide for common and plains garter snakes: https://dnr.wi.gov/topic/EndangeredResources/documents/ButlersIDPoster.pdf