The meridian 121° 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 121st meridian west forms a great circle with the 59th meridian east.
Starting at the North Pole and heading south to the South Pole, the 121st meridian west passes through:
| Co-ordinates | Country, territory or sea | Notes |
|---|---|---|
| Arctic Ocean | ||
| Northwest Territories — Prince Patrick Island | ||
| M'Clure Strait | ||
| Northwest Territories — Banks Island | ||
| Amundsen Gulf | ||
| Northwest Territories — passing through the Great Bear Lake British Columbia — from, passing through Tumbler Ridge | ||
| Washington — passing west of Cle Elum Oregon — from California — from, passing through Modesto (at) | ||
| Pacific Ocean | ||
| Southern Ocean | ||
| Antarctica | Unclaimed territory | |