Pokémon Red, Blue, and Yellow are primarily set in the fictional region of Kanto.
Kanto is the first major region introduced in the Pokémon video game series. Players travel through its towns, routes, caves, and waterways while collecting Pokémon, challenging eight Gym Leaders, and eventually facing the Elite Four and Champion.
The region's name is shared with a real region of Japan, but the Pokémon setting is a fictionalized game world. Several locations and cultural details were inspired by geography around Japan's real Kantō region. The Pokémon anime and later games also revisited Kanto, helping make it one of the franchise's most recognizable settings.
Kanto is sometimes confused with Johto because the two regions appear together in Pokémon Gold, Silver, and Crystal. Johto is the setting introduced in Generation II, while Kanto is the original region from Generation I. The distinction matters because each region has its own towns, Gym Leaders, map design, and regional Pokédex.