From Bulbapedia, the community-driven Pokémon encyclopedia.
Happy Town (Japanese: ハッピータウン Happy Town) is an anime-exclusive town located in Johto. It is located between Cherrygrove City and Violet City.
Shortly before entering Violet City, Ash and his friends needed a place to stay for the night, and they decided to spend the night in Happy Town's Pokémon Center. While there, they learned that this Pokémon Center had a Blissey in charge of operations instead of the usual Chansey. As it turned out, this Blissey was an old friend of Jessie's, since the two had gone to Pokémon Nurse School together.