Asked in Pokemon Diamond Pearl and Platinum
Where can you find eeve in Pokemon diamond?
Both of these require u to get the national dex:
Go to hearthome city. Go into that girl bebe's house (she's the one that made your storage boxes in the PC). She'll give u a lv 5 eevee if u have an empty slot on your team. If u want more eevees to get all of the evolutions, try the suggestion below or breed the eevee that bebe gave to u.
Go to the mansion south of Hearthome. Talk to Mr. Backlot. You know how he tells u what 'rare' Pokemon are in his backyard that day? One of these Pokemon is eevee. If he tells u he saw an eevee, go out into the garden and try to catch one right away.