Records of the western harvest mouse in Illinois are thin and scattered, just 27 since 2000, mostly turning up around Cache River State Natural Area, Chautauqua National Wildlife Refuge, and refuge lands along the upper Mississippi River. Illinois sits near the eastern edge of this mouse’s range, which otherwise runs through California, the Great Plains, and the interior West, so a low record count here likely reflects genuine scarcity at the range’s margin rather than under-searching alone.
The handful of Illinois reports cluster most in November, though with numbers this small, that spike is more a quirk of a few sightings than a real seasonal pattern. NatureServe still lists the species S4, Apparently Secure, statewide.
Wherever it does turn up, this mouse threads through dense grass and marsh edges on narrow runways, climbing stems to clip seeds rather than crossing open ground. Its grooved upper front teeth, the feature its genus name refers to, separate it from the look-alike deer mice and house mice sharing the same weedy cover.
Full species profile
