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 normally available only in these regions. They may also appear globally during certain special events. The majority of regional Pokémon can be caught in the wild in its specific region, but some may also be hatched from Pokémon Eggs obtained in those regions. Some Raid Bosses are also Region-exclusive.

List of region-exclusive Pokémon
Currently in game there are 40 (46 if including evolutions) region-exclusive Pokémon.

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

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

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

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

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

There is currently two region-exclusive Pokémon from the Kalos region:

There is currently four region-exclusive Pokémon from the Alola region:

Migration events
During many events, region-exclusive Pokémon were migrated around to appear outside of their usual region. Sometimes those were just small regions – Pokémon GO Safari Zone, but other times these migrations occur globally – World Tourism Day.

Trivia

 * The Lake Guardians are the first and only regional-exclusive Legendary Pokémon.
 * Mime Jr. is the first and only regional-exclusive Baby 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.
 * Lunatone and Solrock have swapped their regions several times. Check their articles for details.
 * Heatmor was first available in the Americas and Africa and Durant was first available in Europe, Asia and Australia.
 * On November, 2020, they swapped regions. This was unannounced.