The Razor's Edge
The Eladrin in this world do come from the Feywild, but the Feywild is a little different than what would normally be expected. The Feywild is a complete echo plane of the Prime Material plane, but the only crossover areas exist down in the 115 – 118 part of this overview map of Greyhawk.
The Prime Material plane inhabitants, and only a select few at that, have only been aware of the Feywild for approximately 10 years, whereas the Eladrin have been crossing over for nearly 20 years. The Eladrin have been studying the Prime Material inhabitants for these 200 years with a strict eye on the Elves.
Almost nothing is known of the Eladrin or the Feywild on the Prime Material plane as of now.