They are the most widespread rodent in North America, with occurrences in almost every habitat type in Canada, the United States, and Mexico.

Their diet varies with the location. If available they enjoy a variety of seeds, fruits, nuts, and insects. In moist habitats they will also feed on fungi. They keep extra food in caches spread out all over their home range. Some popular places for food caches include hollow logs, tree cavities such as woodpecker holes, bird nests, burrows beneath the ground, and in human litter such as old shoes and mattresses that have been left in deserted areas.

The breeding season varies and is generally determined by rainfall. In areas with long rainy seasons these little critters may breed throughout the entire year. In dryer areas the breeding season begins shortly after the first rain and ends when the temperature begins to rise and the rain stops. Females may have two to four litters each year. Litters may consist of one to six young. Young can begin breeding when they are between five and seven weeks old.

In the wild deer mice rarely live more than one year. Common predators are owls, foxes, coyotes, and bobcats. These little mice look cuddly and are easily handled, but it is a good idea not to touch them. They are the primary host of Hantavirus, plague, and Lyme disease.