The most visible mammal at the park is the white-tailed deer, however, many more utilize the area. Recent surveys found at least 35 mammal species at the park! During the warmer season, thirteen-lined ground squirrel can be observed peeking from their burrows at Mound City Group. The deer mouse apparently enjoys the labors of archeologists as they can usually be found in excavation units. Running among trees and shrubs are the active fox squirrel, gray squirrel, and eastern chipmunk, and sometimes at dusk the southern flying squirrel can be seen soaring above from tree to tree. During the winter months, the meadow vole may be seen darting from one snow-covered hole to the next, perhaps avoiding the smallest carnivore in the world, the least weasel.
Careful study of the summer sky during twilight hours may reveal flying hunters such as big brown bats, eastern red bats, and little brown bats. These species feed on thousands of insects each night. The hoary bat prefers to feed over larger streams. In fact, most bats prefer areas with an available source of water.
Other mammals that may be encountered: Virginia opossum, short-tailed shrew, least shrew, masked shrew, eastern mole, eastern cottontail, woodchuck, beaver, eastern harvest mouse, white-footed mouse, prairie vole, house mouse, muskrat, meadow jumping mouse, coyote, red fox, raccoon, striped skunk, mink, evening bat, northern bat, and eastern pipistrelle.