Regions are an organized areas of the Pokémon world known from previous games about Pokémon such as games from core series. In Pokémon GO there are currently only five regions referred, which are Kanto, Johto, Hoenn, Sinnoh and Alola.
The Pokémon known from Kanto region were the base Pokémon released in Pokémon GO, but not all Pokémon of this region were released at one time.
- Most of the Pokémon from Kanto was released with the game release.
- November 22nd, 2016 – Ditto was released in the games, disguised as other Pokémon.
- July 22nd, 2017 – Articuno was available from Raid Battles for the first time.
- July 31st, 2017 – Moltres was available from Raid Battles for the first time.
- August 7th, 2017 – Zapdos was available from Raid Battles for the first time.
- From August 12th, 2017 to August 31st, 2017 - All three Legendary Birds were available from Raid Battles.
- On August 14th, 2017, during the Pokémon GO Stadium event, Mewtwo was confirmed as a Raid Boss.
- On March 30th, 2018 – Mew became available as the reward for completing Special Research tasks.
Currently only Smeargle is still not available nor officially scheduled to be released.
- December 12th, 2016 - Togepi and Pichu along with other Baby Pokémon (except Tyrogue) and Togetic as evolution of Togepi were released as Pokémon available only to hatch from Pokémon Eggs.
- February 16th, 2017 - over 80 Pokémon from this region became available to catch in the wild and hatch from eggs.
- July 22nd, 2017 - Lugia was released as the Legendary Raid Boss for the first time and were available to catch only after defeating it.
- From August 31st, 2017 to September 30th, 2017 - Legendary Beasts were available as the Legendary Raid Bosses for the first time and were available to catch only after defeating them. All three of these Pokémon were exclusive to following regions:
- On September 30th, all three of Legendary Beasts moved to different locations and are available until October 31st in following regions:
- Raikou could be battled throughout the Asia-Pacific region
- Entei could be battled throughout the Americas
- Suicune could be battled throughout Europe and Africa
- On October 30th, all three of Legendary Beasts moved for last time to different locations and were available until November 31st in following regions:
- Raikou - Europe and Africa
- Entei - Asia-Pacific region
- Suicune - the Americas.
- November 27th, 2017  - Ho-Oh was released as the Legendary Raid Boss for the first time and were available to catch only after defeating it.
- December 20th, 2017 – Delibird was announced to be released along with 20 Ice and Water-type Pokémon from Hoenn.
- It was released day later, on December 21st, 2017.
- On July 14th, 2018 – Celebi became available for Pokémon GO Fest 2018 attendees only.
- On August 20th, 2018 – Celebi became available worldwide as the reward for completing Special Research tasks.
Hoenn is the third region from original core series of which Pokémon are now available in Pokémon GO.
Selected Pokémon from this region were mostly released in 5 waves:
- In October 2017 as a part of Halloween event - 5 Ghost-type Pokémon.
- In December, 2017 as main release of Hoenn-region Pokémon - 50 selected Pokémon.
- In later December, 2017, more Pokémon of this region were made available - 20 aquatic themed, mainly Water and Ice-type Pokémon.
- In January, 2018, yet more were made available - 23 dessert themed, mainly Ground and Rock-type Pokémon.
- In February, 2018, more selected, sky themed, mainly Flying and Dragon-type Pokémon.
Listed waves don't include Hoenn-region Legendary Pokémon that were temporally released as Raid Bosses.
- On October 20th, 2017, five Pokémon of Ghost and Dark types were released as a part of Halloween event. Those were Sableye, Shuppet, Banette, Duskull and Dusclops.
- December 6th, 2017 - 50 selected Pokémon from Hoenn-region were announced to become available to catch in the wild and hatch from eggs later that week along with Weather game feature. 
- December 15th, 2017 - Groudon was available to be defeated and caught in Raid Battle for the first time. 
- On December 20th, 2017 - 20 Water and Ice-type Pokémon from Hoenn region were announced to catch in wild and they were released day later.
- January 12th, 2018 - Kyogre was available to be defeated and caught in Raid Battle for the first time.
- On January 23rd, 2018 - 23 mostly Rock and Ground-type Pokémon from Hoenn region were announced and later this day released to catch in wild.
- On February 8th, 2018 - 19 mostly Flying and Dragon-type Pokémon from Hoenn region were announced to catch in wild and they were released day later. 
- February 9th, 2018 - Rayquaza was available to be defeated and caught in Raid Battle for the first time. 
- April 2nd, 2018 - Latios was able to be defeated and captured across the Americas and Africa for the first time; until it switched with is counterpart Latias, which is now available in Europe and Asia.
- May 9th, 2018 - Latias is able to be defeated and captured across the Americas and Africa for the first time; while is counterpart Latios is available in Europe and Asia.
- June 22nd, 2018 - Regice was available to be defeated and caught in Raid Battle for the first time.
- July 20th, 2018 - Registeel was available to be defeated and caught in Raid Battle for the first time.
- August 2nd, 2018 - 8th pattern form of Spinda was made available as reward for Field Research tasks. 
- August 17th, 2018 - Regirock was available to be defeated and caught in Raid Battle for the first time.
- October 1st, 2018 - Deoxys became available to be battled exclusively in EX Raid Battles.
- November 1st, 2018 – Nincada, Ninjask, Shedinja were exclusively released with the Bug-type Pokémon themed Research tasks. Nincada became reward for regular Field Research tasks, while Shedinja could be rewarded from Field Research Breakthrough.
Alola is the fourth region, in release order, to be mentioned in Pokémon GO. Unlike three previous regions there are currently no Pokémon from this region planned to be added to the game but only Alolan forms of Kanto-region Pokémon.
- May 21st, 2018 - The release of Alolan forms of Kanto-region Pokémon was announced to be released in game. 
- May 29th, 2018 - Alolan Exeggutor was released.
- June 22nd, 2018 - Alolan variants of Vulpix, Sandshrew, Meowth, Grimer and their evolutionary lines were made available to hatch from 7-km Eggs. 
- June 23rd, 2018 - Without prior announcement, Alolan Rattata became available to be caught in the wild. 
- July 14th, 2018 - Alolan variants of Geodude, Diglett and their evolutionary lines were released to catch in the wild with the beginning of 2018 edition of Pokémon GO Fest. 
- They were added to 7-km Eggs hatchlings pool after the event has ended.
- July 20th, 2018 - Alolan variants of Raichu and Marowak were made available to be defeated and caught in Raid Battle.
Sinnoh is the fifth region from which Pokémon are available in Pokémon GO. Pokémon originaly discovered in this region are going to be released in waves, similarly to Hoenn-region Pokémon release.
- October 9th, 2018 – Release of Sinnoh-region Pokémon was officially announced. 
- October 16th, 2018 – 26 select Pokémon were released to the gameplay.  Including:
- Turtwig, Chimchar, Piplup, Starly, Bidoof, Kricketot and Buneary started appearing in the wild and to hatch from Eggs.
- Shinx and Riolu started to hatch from Eggs.
- Bidoof, Kricketot, Buneary and Shinx became available as Raid Bosses.
- Carnivine was reported to appear exclusively in Southern areas of the United States.
- Chatot was reported to appear exclusively in countries of Southern Hemisphere.
- Pachirisu was reported to appear exclusively in North-Arctic countries (Canada, Northern Russia).
- October 23rd, 2018 – 6 select Ghost- and Dark-type Pokémon were released to the gameplay. Including
- November 6th, 2018 – Budew, Buizel, and Floatzel were released, but not Roserade.
- Another term used in Pokémon GO players community to describe Pokémon groups from each region is Generations. This term was adopted by community but it is not correct in context of Pokémon GO game as the game itself does not have generations as a result of being under ongoing development. This term wasn't officially referred in game nor by its creators on official social-media and information channels.
- Therefore Kanto is Generation I, Johto is Generation II, Hoenn is Generation III and so on.
- More about generations is available here.
- Common thing for Pokémon, that were not available with main release of Kanto- and Johto-region Pokémon, is that those Pokémon either were legendary and/or mythical or have certain, special moves like Ditto, Delibird or Smeargle.
- Pokémon from Hoenn region although didn't have their one main release as they were released in smaller groups.
- There has been Pokémon species from Hoenn added to game code since update 0.71.0.
- On December 5th, 2017 in Apple Watch Store, Pokémon GO banner with Starter Pokémon from Hoenn region appeared- spoiling official announcement about release of Hoenn-region Pokémon that happened next day. 
- Release of fifty Pokémon from Hoenn region and Weather feature had trailer with similar cinematic style as trailer for release of Legendary Pokémon in raid battles and new gyms system and trailer of the game itself.
- On October 9th, 2018, Pokémon from Sinnoh region were announced to be released.
- There are at most sixteen known regions that have appeared in the various Pokémon canons.
- ↑ Mewtwo Spotted at the Stadium!. /r/TheSilphRoad. Retrieved on 2017-08-14.
- ↑ Ho-Oh will be available to battle for an additional 48 hours Retrieved on 2017-12-06.
- ↑ Introducing Weather and 50 Pokémon from the Hoenn Region in Pokémon GO! Retrieved on 2017-12-06.
- ↑ PokemonGOApp - Trainers, dozens of Pokémon originally from the Hoenn region have been spotted all over the world! - Twitter Retrieved on 2017-12-11.
- ↑ Groudon Appearing in Raid Battles around the World! Retrieved on 2017-12-20.
- ↑ Kyogre Appearing in Raid Battles around the World! Retrieved on 2018-01-13.
- ↑ 7.0 7.1 Discover Rayquaza and More Pokémon Originally from the Hoenn Region! Retrieved on 2018-02-08.
- ↑ Anybody verify if other Spinda are available my player group all got number 8 Retrieved on 2018-08-02.
- ↑ new spinda pattern? #3 Retrieved on 2018-09-02.
- ↑ New Spinda form #1 Retrieved on 2018-10-02.
- ↑ Alolan Forms of Pokémon Originally Discovered in the Kanto Region Are Coming to Pokémon GO! Pokémon GO Live. Retrieved on 2018-05-24.
- ↑ PokemonGoApp. Alola, Trainers! 🌴 As excitement builds for Pokémon: Let’s Go, Pikachu! and Pokémon: Let's Go, Eevee!—coming in November to Nintendo Switch—Alolan Exeggutor has arrived!. Twitter. Retrieved on 2018-05-29.
- ↑ PokemonGoApp. Alola, Trainers! 🌴 Professor Willow has confirmed reports of Alolan Pokémon hatching from Eggs that were gifted by another Trainer. Twitter. Retrieved on 2018-06-27.
- ↑ u/LegoGunnar13 Alolan Rattata appearing on my sightings! r/TheSilphRoad. Retrieved on 2018-06-27.
- ↑ Global Research, Pokémon Sightings, and More Coming During Pokémon GO Summer Tour 2018! Pokémon GO Live. Retrieved on 2018-06-27.
- ↑ 16.0 16.1 The Adventure Continues–Pokémon Originally Discovered in the Sinnoh Region are here! Pokémon GO Live.
- ↑ Community Note: Upcoming Changes to Pokémon GO Pokémon GO Live.
- ↑ Gen 3 in Apple Watch store! (With minor typo) /r/TheSilphRoad. Retrieved on 2017-12-05.
- ↑ Community Note: Upcoming Changes to Pokémon GO. Pokémon GO Live. Retrieved on 2018-10-09.