There is a low vertebral keel on the back that becomes less prominent with age. The marginals on the rear of the carapace are serrated. The plastron is dull yellow with some black or dark pigment. The head and limbs are black or dark olive. There are light lines on the head and limbs that also form a map like pattern.
Females grow much larger than the males.
Adult females have a low keel on the back, large heads, and a light upper lip. Adult males have a pronounced keel on the back, dark upper lips, long claws on the front feet, and a long, thick tail with the cloacal opening past the edge of the carapace. Young have brighter shells and markings, a dark pattern on the plastron, and a pronounced vertebral keel. The common map turtle has been documented along the Mississippi River and tributaries in extreme eastern Iowa. This turtle is found only in slow portions of larger rivers in Iowa.