What was the first Pokémon game region called?

The first Pokémon game region was called Kanto.

Kanto is the setting for Pokémon Red, Green, Blue, and Yellow. It contains locations such as Pallet Town, Viridian City, Celadon City, and the Pokémon League, as well as eight Gyms led by trainers including Brock, Misty, and Sabrina.

The region is based partly on Japan's real Kantō region, which includes Tokyo and surrounding prefectures. Pokémon's fictional geography uses recognizable ideas from Japan while adding routes, caves, forests, islands, and other game-specific locations.

Kanto is sometimes mistaken for the entire first-generation setting, but it is the region rather than the generation itself. The first generation is the broader game era, while Kanto is its principal world and home to the original 151 Pokémon.