It ranges from Ontario west to Alaska, and south to Missouri, north-central Nebraska, the northern half of Wyoming, and central Washington south through Idaho into north-central Utah. A disjunct subset of its range occurs from central Colorado to northwestern New Mexico. An isolated population was formerly found in Chihuahua, Mexico, but has since been extirpated. The United States portion of the Souris River is alternately known as the Mouse River because of the large numbers of field mice that lived along its banks.