To date, 35 species of mammals are known to call Crescent Lake NWR home. These include a variety of small mammal groups that include shrews, moles, ground squirrels, pocket gophers, mice, rats, and voles. Larger mammals include the Porcupine, Muskrat, Raccoon, and six members of the carnivorous weasel family including the Badger. The Coyote is the most commonly encountered canid on the Refuge, while surveys to detect the State Endangered Swift Fox were undertaken in June of 2014. Crescent Lake is also home to Pronghorn and both Mule and White-tailed Deer.
Historically, species such as the Elk, Bison, Plains Grizzly Bear, Plains Wolf, Black-footed Ferret, and Black-tailed Prairie Dog occurred in the area. Today, Black-tailed Prairie Dogs are seldom located on the Refuge but can be found on adjacent lands. The aforementioned Swift Fox surveys will help determine if this diminutive fox is still present at Crescent Lake NWR.