How many Eevee evolves are there?

Seven.

Eevee evolves INTO Vaporeon using a Water stone.

Eevee evolves INTO Flareon using a Fire stone.

Eevee evolves INTO Jolteon using a Thunder stone.

Eevee evolves INTO Espeon when it reaches full happiness in the Daytime

Eevee evolves INTO Umbreon when it reaches full happiness in the Nighttime

Eevee evolves INTO Leafeon near the rock in Eterna Forest

Eevee evolves INTO Glaceon near the rock in Route 217