From Bulbapedia, the community-driven Pokémon encyclopedia.

HopHopHop Town (Japanese: ヨヨヨタウン Yoyoyo Town) is a location that only exists in the Pokémon anime. It is located just outside of Celadon City.

HopHopHop Town was featured in the episode Hypno's Naptime. Ash and his friends learned that several children had gone missing in the city, and several Pokémon were suffering from fatigue. With the help of Officer Jenny, they were able to discover the source of the problem; a group of people suffering from insomnia were using a Hypno to help them fall asleep. After Misty was hypnotized by it, she ran into a park, where all the missing children were discovered, thinking they were Pokémon. Using Drowzee, the children were cured and sent home to their parents.

In addition, HopHopHop Town is also where Misty captured her Psyduck. Brock promised Nurse Joy he would take care of it, but changed his mind. Psyduck captured itself inside of one of Misty's Pokéballs, making it hers.

Anime- and Special-exclusive locations in Kanto

A.J.'s Gym | Cerise Island | Chrysanthemum Island | Camomile Island | Crimson City | Dark City | Fennel Valley | Frodomar City | Gaiva Dam | Gardenia Town | Grandpa Canyon Gringey City | Hidden Village | HopHopHop Town | The House of Imite | Kas Gym | Leaf Forest | Maiden's Peak | Mossgreen Village | Mulberry Town | Mt. Hideaway Neon Town | New Island | Pokémon Land | Pokémon Tech | Porta Vista | Potpourri Island | Rifure Village | Rota | Sayda Island | Scissor Street | Silver Town | Stone Town Sunny Town | Terracotta Town | Tree of Beginning | Wisteria Town | Yas Gym