Pokémon's first games, Pocket Monsters Red and Green were released on Tuesday, February 27th, 1996. As a way to thanks all the fans, The Pokémon Company got the Japanese Memorial Day Association to officially recognize February 27th as "Pokémon Day" in Japan!

The latest information about Pokémon will be announced on Pokémon Day on Thursday, February 27th, 2020! To commemorate "Pokémon Day", a special Max Raid Battle will be held in the Nintendo Switch games "Pokémon Sword and Shield"! There are also in-game events planned for the smartphone app “Pokémon GO”.

Also, a new Mythical Pokémon will be revealed for Pokémon Sword and Shield! This Pokémon will also appear in the movie "Pocket Monsters Coco", which is scheduled to be released on July 10th, 2020. More detailed information about this Pokémon's appearance will be revealed on Pokémon Day! In addition, the latest information on the smartphone app “Pokémon Masters” will be announced.

Source: https://www.pokemon.co.jp/info/2020/01/200131_cm01.html