Where to find every legendary Pokémon in Pokémon Red

Pokémon Red has five legendary Pokémon: Articuno (Lv 50), Zapdos (Lv 50), Moltres (Lv 50), and Mewtwo (Lv 70), plus Mew. Each one appears once, so save before the battle.

Articuno, level 50

Seafoam Islands (B4F): it waits on the bottom floor of the Seafoam Islands. Catch rate 3 of 255: bring Ultra Balls and use sleep or paralysis, or save the Master Ball for it.

Zapdos, level 50

Power Plant: it roosts at the far end of the Power Plant. Catch rate 3 of 255: bring Ultra Balls and use sleep or paralysis, or save the Master Ball for it.

Moltres, level 50

Victory Road (2F): it sits in Victory Road on the way to the Indigo Plateau. Catch rate 3 of 255: bring Ultra Balls and use sleep or paralysis, or save the Master Ball for it.

Mewtwo, level 70

Cerulean Cave (B1F): it waits at the bottom of Cerulean Cave after you become Champion. Catch rate 3 of 255: bring Ultra Balls and use sleep or paralysis, or save the Master Ball for it.

Mew

Mew was never meant to be caught in Red, but the trainer-Fly glitch makes a wild level 7 Mew appear.