Where do you find a tentacool on emerald?

You can find Tentacool in the following locations in Pokémon Emerald:

* Route 119: Tentacool are common here, especially in the water.

* Route 120: You can find them here as well, though they are less common than on Route 119.

Tentacool is a Water-type Pokémon, so it will prefer to be in water areas. It is also a relatively common encounter, so you should have no trouble finding one in these locations.