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.

From Pole to Pole

Starting at the North Pole and heading south to the South Pole, the 123rd meridian west passes through: ! scope="col" width="130" | Co-ordinates ! scope="col" | Country, territory or sea ! scope="col" | Notes ! scope="row" style="background:#b0e0e6;" | Arctic Ocean ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | M'Clure Strait ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | Amundsen Gulf ! scope="row" | 🇨🇦 ! scope="row" style="background:#b0e0e6;" | Boundary Bay ! scope="row" | 🇺🇸 ! scope="row" style="background:#b0e0e6;" | Strait of Juan de Fuca ! scope="row" | 🇺🇸 ! scope="row" style="background:#b0e0e6;" | Pacific Ocean ! scope="row" | 🇺🇸 ! scope="row" style="background:#b0e0e6;" | Pacific Ocean ! scope="row" | 🇺🇸 ! scope="row" style="background:#b0e0e6;" | Pacific Ocean ! scope="row" style="background:#b0e0e6;" | Southern Ocean ! scope="row" | Antarctica