Years ago I remember my aunt telling me that FAO Schwarz was the oldest toy store in the city, from the 1860s. Not only do I not know if that's true, I don't think it fits into the oldest dept. store category. But hey, the prize money sounds good so I gave it a shot.
Sorry 28th, but if Charlie is offering 500 bucks for the answer, I have to go with MacTAC.
Sorry Charlie, I couldn't resist LOL!!!