The meridian 42° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Greenland, the Atlantic Ocean, South America, the Southern Ocean, and Antarctica to the South Pole.
The 42nd meridian west forms a great circle with the 138th meridian east.
Starting at the North Pole and heading south to the South Pole, the 42nd meridian west passes through:
| Co-ordinates | Country, territory or sea | Notes |
|---|---|---|
| Arctic Ocean | ||
| Lincoln Sea | ||
| Nansen Land | ||
| J.P. Koch Fjord / Navarana Fjord | ||
| Freuchen Land | ||
| Atlantic Ocean | ||
| Maranhão Piauí — from Bahia — from Minas Gerais — from Rio de Janeiro — from, the mainland and Ilha do Cabo Frio | ||
| Atlantic Ocean | Passing just east of the Shag Rocks, (at) Passing just west of Black Rock, (at) | |
| Southern Ocean | ||
| Antarctica | Claimed by both (Argentine Antarctica) and (British Antarctic Territory) | |