Cotton rats have relatively large eyes.
The ears are large but almost hidden in the fur. They have four toes plus a small thumb on their front feet and five toes on each hind foot. The cotton rat has very small internal cheek pouches. Distinguishing characteristics are the rough grizzled appearance of the blackish or grayish fur with rather stiff black guard hairs. The cotton rat may be distinguished from the Norway rat by its smaller size, shorter tail, and longer grizzled fur.