Males are slightly larger than females. Woodchuck skulls are broad and flat. Strongly developed supraorbital processes project at right angles from the frontals with the tips projecting slightly forward. The dense, woolly underfur of the back and sides of the woodchuck is somewhat obscured by longer, less dense guard hair. The underfur of the woodchuck is gray with yellow tips, much paler from the dorsal area.
Ears are small, low and rounded atop a black-colored head with small black eyes.
There is one annual moult from late May to September, which begins at the tail and progresses forward. The feet are black and slightly flattened. The hind foot has five well-developed digits. The rudimentary first digit of the forelimb is covered by a flat nail. All other digits terminate in curved claws that are useful in digging.