Umbreon evolves from Eevee, a Pokemon specially designed to evolve into several different types of Pokemon. Umbreon is its Dark version.
Eevee doesn't evolve into Umbreon at any specific level - there are only two ways that you can get an Umbreon in the game without trading. One is to spoil your Eevee senseless and, if it begins to try and evolve during the day, keep it an Eevee and level it up at night; if you let it evolve during the day it will be an Espeon.
The other way to evolve an Umbreon is to use a Moon Shard on it, though this option is only available in Gale of Darkness.