The meridian 109° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole.
The 109th meridian west forms a great circle with the 71st meridian east.
In the United States, the western boundaries of Colorado and New Mexico and the eastern boundaries of Utah and Arizona lie on the 32nd meridian west from Washington, which is approximately 3 minutes of longitude west of the 109th meridian west of Greenwich, or approximately .
Starting at the North Pole and heading south to the South Pole, the 109th meridian west passes through:
| Co-ordinates | Country, territory or sea | Notes |
|---|---|---|
| Arctic Ocean | Passing just east of Borden Island, Nunavut, Canada (at) Passing just east of Vesey Hamilton Island, Nunavut, Canada (at) | |
| Canada | Nunavut — Melville Island | |
| Sabine Bay | ||
| Canada | ||
| Parry Channel | Viscount Melville Sound | |
| Canada | Nunavut — Victoria Island | |
| Dease Strait | ||
| Bathurst Inlet | ||
| Canada | Nunavut — Lewes Island, the Stockport Islands and the mainland Northwest Territories — from, passing through the Great Slave Lake Saskatchewan — from, passing through Lake Athabasca | |
| United States | Montana Wyoming — from Colorado — from New Mexico — from | |
| Mexico | Sonora Sonora / Chihuahua border — from Sonora — from Sinaloa — from, passing through Los Mochis | |
| Pacific Ocean | Passing just east of Clipperton Island (an overseas possession of France, at) Passing just east of Easter Island, Chile (at) | |
| Southern Ocean | ||
| Antarctica | Unclaimed territory | |