Region-exclusive Pokémon

Region-exclusive Pokémon, also known as regional Pokémon, are group of Pokémon that are exclusive for specific regions in the real world and are available only by encountering them in wild and getting their Eggs in these specific regions.

Currently in game there are 33 (37 if including evolutions) region-exclusive Pokémon.

Kanto
There are four region-exclusive Pokémon from the Kanto region:

Johto
There are two region-exclusive Pokémon from the Johto region:

Hoenn
There are nine region-exclusive Pokémon from the Hoenn region:

Sinnoh
There are currently eight (nine if including Gastrodon) region-exclusive Pokémon from the Sinnoh region:

Unova
There are currently ten (13 if including evolutions) region-exclusive Pokémon from the Unova region:

Trivia

 * The Lake Guardians are the first regional-exclusive Legendary Pokémon.

Historical trivia

 * Farfetch'd started to appear globally around 05:00 PM PST, as the reward of Global Catch Challenge, for 48 hours starting on November, 2017.
 * It was available to capture in the wild and could also be summoned with Lure Modules and Incense.
 * On January, 2018, Zangoose was region-exclusive Pokémon mostly for the Western Hemisphere and Africa and Seviper was exclusive mostly for the Eastern Hemisphere despite of Africa. After that day they were swapped.
 * On February, 2018, Minun and Plusle just like Zangoose and Seviper were exclusive to two opposite hemispheres, after that day, they stopped being region-exclusive Pokémon.
 * On June, 2018, Solrock and Lunatone swapped regions to celebrate the Summer Solstice.
 * On March, 2019, Solrock and Lunatone swapped regions again to celebrate the Equinox.