The meridian 123° 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 123rd meridian west forms a great circle with the 57th meridian east.
Starting at the North Pole and heading south to the South Pole, the 123rd 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 just east of Vancouver (at) | ||
| Boundary Bay | ||
| Washington — Orcas Island, Shaw Island and San Juan Island | ||
| Strait of Juan de Fuca | ||
| Washington Oregon — from, passing through Salem (at) California — from | ||
| Pacific Ocean | ||
| California — Point Reyes | ||
| Pacific Ocean | ||
| California — Southeast Farallon Island | ||
| Pacific Ocean | ||
| Southern Ocean | ||
| Antarctica | Unclaimed territory | |