From Bulbapedia, the community-driven Pokémon encyclopedia.
Arborville (Japanese: ハテノ村 Hateno Village) is a small town in Johto that was visited by Ash, Brock, Misty and Sammy in Celebi: Voice of the Forest. It is located in a big forest. All houses in it are built in trees. It is home to the same woods where the Celebi and the Suicune from the fourth movie live.
It bears a remarkable similarity to the game version of Fortree City (first featured in Pokémon Ruby and Sapphire three years later). Just like Fortree City, all of Arborville's houses are built in trees. According to anime maps, Arborville is located just north of Olivine City. Known residents of Arborville include Towa, Diana, and Mr. White.