You can get Eevee in Celadon City’s Mansion. Enter the back door of the mansion and climb up to the topmost floor to find a Poké Ball on the table with Eevee inside.

Getting Eevee

There aren’t any prerequisites for getting Eevee, so it’s possible to get it mid-game as long as you already have access to Celadon City. If you haven’t gotten Eevee yet on your first visit to Celadon, head there now to get to the Pokémon Mansion, highlighted in the map below.

From the Pokémon Center, go up the opening immediately to the right and follow the path ahead.

You’ll see the tall building that is the Celadon Mansion and find that there’s a backdoor entrance to it like so.

Head inside and climb up the steps. You need to do this three times until you reach the rooftop.

Go down a bit to find the entrance to another room. There’s a man inside that talks about wireless trading, as well as resources about it written on the board. There’s also a TM book on the table. The key item here, however, is the Poké Ball on the table.

Click on it to get Eevee. It’s as simple as that!

Eevee will be at Level 25 when you get it and will have the following move set.

Training Eevee

Eevee may not seem much at first glance, but it is one of the most versatile Pokémon you can have in-game.

On its own, Eevee is a Normal-type Pokémon with a simple move set upon level up: Quick Attack, Baton Pass and Take Down, among others.

However, what makes Eevee special is its unique trait of evolving into either one of three elemental forms: Flaeron, Jolteon and Vaporeon. Here’s a detailed article on how to evolve Eevee and get all of its evolutions.

Take note however that Eevee cannot be found in the wild. That said, you can get another Eevee in the game through trading or by breeding it in Four Island’s Daycare Center, but that’s only available in the later stages of the game.