A wee bit of help
The best source for this info is the old gray box.
I'm going from memory here, as I don't have the box in front of me at the moment, but I seem to recall the continent of Faerun being somewhat larger than the contiguous US by maybe 30-50% (there's a nice picture of it in the Cyclopedia). Given the large number of states in that area, look to Europe for comparably sized nations.
Advice: Even if you run a strictly 3E campaign, pay for the ESD of the original FR campaign setting (the gray box). The source material is largely independent of game mechanics, and very well worth the money, even though much of it is out of date.
