How Do You Evolve Eevee In Pokemon Platinum?

Keep your Eevee with you and go to the Eterna forest, there is a mossy rock there level up your eevee near the rock (I think you can evolve it anywhere in the Eterna forest I might have done it before and it wasn't too close to the rock) and TA-DA there's your leafeon.

Flareon" Fire stone on an Eevee
vaporeon" water stone on an Eevee
jolteon: Thunder stone on an Eevee
Espeon: Train Eevee during morning (I don't know the specific time sorry....)
Umbreon: Train Eevee during nighttime (I don't know the specific time sorry....)Leafeon: Level up Eevee by the mossy rock in eterna forestGlaceon: Level up Eevee by the icy rock in route 217

You level it in eterna forest and level it up once. Bingo. 1 leafeon.

Fire stone for a flareon
water stone for vaporeon
thunder stone for jolteon
level it up by the mossy rock in eterna forest for leafeon
level it up by the icy rock in route 217 for glaceon

This doesn't answer the question but you can find an eevee after you beat the elite four and get the national pokedex go to the stately pokemon Mansion and talk to the owner till he says that he saw a eevee in the garden

You can use a fire, water and thunder stone(flareon,vaporeon and jolteon).... Level up at eterna forest(leafeon), level up at route 216(glaceon) and increase happiness level and level up during day (espeon) and night(umbreon)

How do you no if your pokemon r fully happy I'm trying 2 evolve my eevee in2 umbreon but I don't no wen 2 do it because I don't know wen its fully happy

You need to find some stones

I did what you said dude

Vaporeon: Use a water stone on Eevee
Flareon: Use a fire stone on Eevee
Jolteon: Use a thunder stone on Eevee
Espeon: Train during daytime
Umbreon: Train during nighttime

Go to eterna forest and get to the stone and evolve it there

also I have 4 cranidos's does any1 want to trade?

Level Eevee up at the rock in Eterna Forest. It's in the top upper right hand corner.

Flareon: Fire stone
Vaporeon:Water stone
Jolteon:Thunder stone
Umbreon: Happy at night
Espeon: Happy in day
Glaceon: Level up by Ice rock (route 217)
Leafeon: Level up near moss rock (eterna forest)

Use a water stone for vaporeon, a fire stone for flarion, a thunder stone for jolteon, train during day for espeon, and train during night for umbreon.

 Ok thanks,guest.
 
 I just thought I couldn't evolve my eevee into leafeon because,well,I actually have two eevee's.
I have action replay and I battled a pokemon breeder that was a girl.fist I defeated her Bu dew then she sent out a female eevee and I just had to catch it and way before that,I put action replay in my DS and did these cheats:
*Walkthrough walls
*Capture Trainer Pokemon
I forgot the last one,but I'm talking about the "Capture Trainer Pokemon" cheat. So I captured her female eevee and had two eevee's and I was lucky because it would've said,
"Would you like to give a nickname to the Bad Egg?"
Yeah,that could've happened.
But don't you ever wonder what a Bad Egg hatches into?
It could be a Missing no.,M,---- anything!But I"m totally not going to try to figure it out! No way!