Pokémon Red and Blue are set primarily in the fictional region of Kanto.
Kanto is the setting for the first-generation Pokémon adventure, where players travel between towns, challenge eight Gym Leaders, and attempt to become Pokémon League Champion. It is also the home region of the original 151 Pokémon.
The region's locations include Pallet Town, Viridian City, Pewter City, Cerulean City, and Saffron City. Many of these names became foundational parts of Pokémon's geography.
Kanto is sometimes confused with Johto because the two regions are connected in Pokémon Gold and Silver. In the original Red and Blue games, however, the journey is centered on Kanto alone.