I caught an Eevee, which of its evolutions will it evolve into?
According to this post on the /r/pokemongo subreddit, you can force your Eevee to evolve a certain way by changing its nickname before evolving it to:
- Pyro to evolve into Flareon.
- Sparky to evolve into Jolteon.
- Rainer to evolve into Vaporeon.
(These are the names of Eevee Brothers from the TV series/Manga)
You can also, as of the Generation II update, use nicknames to evolve into a certain Eeveelution, but like before, this works only once.
- Tamao to evolve into Umbreon.
- Sakura to evolve into Espeon.
This now works with the Generation IV evolutions Leafeon and Glaceon. When renaming Eevee the first time, the evolve button with display the evolution it will evolve into rather than a question mark.
- Linnea to evolve into Leafeon
- Rea to evolve into Glaceon
This technique will only work once per evolution. For example, if you have already evolved an Eevee named Rainer into a Vaporeon, evolving another Eevee named Rainer will result in a random evolution.
Evolving without the naming tricks will give you Flareon, Jolteon or Vaporeon by random chance.
Also, according to another reddit thread, by walking 10km with Eevee as a buddy you will get Espeon when evolving during the day and Umbreon when evolving during the night.
Evolution stones as you know them (water, fire, etc.) don't exist in the current version of Pokémon GO. By default, when you evolve an Eevee in Pokémon GO, the evolution is chosen randomly from the first set of potential "eeveelutions" (Vaporeon, Jolteon, Flareon).
To get other Eeveelutions like Espeon/Umbreon, other requirements must be met. See @MBorg's answer for more details.
There is also a method for forcing a specific evolution by giving your Eevee a certain nickname before it evolves. See @Brant's answer for more details.
Vaporeon, Jolteon, Flareon
Evolving an Eevee without meeting any other requirements/prerequisites, will randomly result in either a Vaporeon, Jolteon, or Flareon with a 1/3 chance of either of them.
Espeon, Umbreon
If you keep Eevee as your buddy for 10km, earn at least 2 candy with it whilst it's your buddy, and then evolve it whilst it's your buddy, it will evolve into either:
- Espeon if evolved during the day.
- Umbreon if evolved during the night.
The 10km and 2 candy requirement is counted across all buddy uses of Eevee. You can earn the kilometers and candy, either intermittently or all at once, whilst changing buddies or keeping it the same.
As long as a total of 10km and 2 candy has been earned whilst Eevee has been a buddy, and you evolve it whilst the Eevee is currently set to your buddy.
Day vs night is determined by the game screen in the overworld/map. It's daytime when it is bright, and nighttime when it's dark:
The times when the game screen changes over varies depending on your GPS and time location.
Leafeon, Glaceon
If you purchase a Moss or Icy Rock from the shop (for 200 coins), place it on a Pokestop (like a Lure), spin the Pokestop, and then evolve Eevee whilst in the radius of the Rock, it will evolve into Leafeon (Moss Rock) or Glaceon (Icy Rock).
The silhouette of Leafeon/Glaceon will appear if these requirements are met prior to evolution - if it doesn't, the requirements are not met and it would evolve into Vaporeon/Jolteon/Flareon.
You can also choose a nickname to force a specific evolution, but this only works once per nickname/evolution.