[2] The Illinois Natural History Survey describes the Chicago garter snake as a medium-sized, up to 100 cm (39 in) in total length, including the tail), dark brown or black snake with a yellow or gray mid-back stripe, a yellow stripe on each side, and a gray-green belly with dark spots on the edges of most of the belly scales.

It is a cold-tolerant snake that occasionally emerges from hibernation to bask on warm winter days.

The snake emerges from hibernation upon the spring thaw (March or April), and typically mates immediately after.

The females, like other garter snakes, give birth to a clutch of 15–80 live young; parturition is typically in July through early October.

[2] Its diet includes fish, amphibians, young birds, and invertebrates such as earthworms, slugs, and snails.