Thamnophis elegans, commonly known as the Western Terrestrial Garter Snake, is native to North America. Its geographical distribution spans the western United States, western Canada, and parts of northern Mexico. Key areas include states such as California, Nevada, Oregon, Washington, Idaho, Montana, and Canadian provinces like British Columbia and Alberta.

The Western Terrestrial Garter Snake inhabits a variety of environmental conditions. It is commonly found in grasslands, woodlands, forests, and areas near streams, lakes, and wetlands. The species favors areas with abundant cover, such as fallen logs, rocks, and dense vegetation. The climate in its habitats ranges from temperate to semi-arid, depending on the specific geographical area.

Thamnophis elegans plays a role in its ecosystem as both predator and prey. Its diet primarily consists of amphibians, small fish, earthworms, and occasionally small mammals. This species is well adapted to its environment with its ability to thrive in diverse ecosystems and its resistance to the toxins of some amphibian prey. It often occupies the ecological niche of controlling the populations of its prey species.