Southern bog lemmings are small voles, weighing 20 to 50 g and measuring 110 to 140 mm in total length. The fur on the back ranges in color from a reddish to dark brown and has a grizzled appearance. The belly is silver-gray. They have broad incisors that are grooved, which is helps distinguish southern bog lemmings from other voles. The tail is short, barely longer than the hind foot. They have 4 toes and 1 small, nailed thumb on the forefeet and 5 toes on the hind feet. Fresh vegetation, especially the leaves, stems, seed heads, and roots of grasses and sedges, is the main food of this species. Raspberries, blueberries, and other fruits, insects, fungi, and bark form a lesser part of the diet.

Despite their name, southern bog lemmings are not purely southern, nor do they live only in bogs. Some live in different types of habitats, from prairie grasslands to areas featuring more sedges. In the Northeast, they live spruce forests and dwarf shrub bogs. Southern bog lemmings create surface runways in grassy conditions. They use their sharp teeth to cut grasses, allowing stalks to form concealed corridors of safety. In the northeast, southern bog lemmings also underground tunnels, as well as tunnels through moss in boggy areas.