The species is most common east of the Rocky Mountains, and is absent from much of the western United States, including Nevada, Utah, California, Hawaii, and Alaska (though its close relatives, the mule deer and black-tailed deer Odocoileus hemionus, can be found there). It does, however, survive in aspen parklands and deciduous river bottomlands within the central and northern Great Plains, and in mixed deciduous riparian corridors, river valley bottomlands, and lower foothills of the northern Rocky Mountain regions from South Dakota and Wyoming to southeastern British Columbia, including the Montana Valley and Foothill grasslands.
The conversion of land adjacent to the northern Rockies into agriculture use and partial clear-cutting of coniferous trees (resulting in widespread deciduous vegetation) has been favorable to the white-tailed deer and has pushed its distribution to as far north as Prince George, British Columbia. Populations of deer around the Great Lakes have also expanded their range northwards, due to conversion of land to agricultural uses favoring more deciduous vegetation, and local caribou and moose populations. The westernmost population of the species, known as the Columbian white-tailed deer, once was widespread in the mixed forests along the Willamette and Cowlitz River valleys of western Oregon and southwestern Washington, but today its numbers have been considerably reduced, and it is classified as near-threatened. The white-tailed deer is well-suited for its environment. Fossil records indicate that its basic structure has not changed in four million years.[citation