To this day, Eevee remains a fan favorite in Pokemon Go. Eevee has become so popular it was one of the two starter Pokemon in Let's Go.
Eevee evolution names
When evolving Eevee in Pokemon Go it is random as to whether it will evolve into either Vaporeon, Jolteon, Flareon, Espeon or Umbreon.
That is, it's random unless you know this one simple trick. You don't need to evolve multiple Eevees in order to complete your collection.
In traditional Pokemon games, Eevee is evolved into its desired form by using additional items. For example a water stone would evolve it into Vaporeon.
Pokemon Go works differently where, by default, the Eevee evolution is random between Vaporeon, Jolteon and Flareon. However, if you change your Eevee's name (nickname) it will be guaranteed to evolve into the following.
Choose your Eevee evolution
Now we know the required names to guarantee your desired Eevee evolution, here are the step by step instructions.
This trick only works once. Therefore, once you evolve an Eevee using any of these names, using the same nickname again will result in a random evolution.
Espeon and Umbreon - Day and Night?
In addition to the nickname trick, there's another way you can guarantee an Espeon or Umbreon evolution.
Going all the way back to generation 2, and more specifically Pokemon Gold and Silver, the time of day, rather than evolution stones, determines which Eevee evolves into.
During the night (6pm to 4am by the game clock) would result in an Umbreon. Conversely, the other 14 hours during the day, would cause an Espeon evolution.
The same methodology applies to Pokemon Go also. Firstly, make sure the Eevee you're evolving is your buddy Pokemon and that it has found two berries. This is achieved by walking 10km. Various forum posts state that if these requirements are met, that evolving it during the night will get you an Umbreon, and during the day an Espeon.
More eeveelutions - Leafeon and Glaceon
A further two "eeveelutions" were added to the 4th generation of Pokemon. They were the grass-type Leafeon and ice-type Glaceon.
The majority of the Gen 4 Pokemon have been made available in Pokemon Go. Nevertheless, 27 still remain and this includes Leafeon and Glaceon.
They are expected to be released soon and it remains to be seen whether there will be any interesting tricks to force their evolution.