After years of speculation, I actually know the real answer! How? There is an episode where the couch gag has Homer sitting there and the camera pans out continuously, until it zooms out of Springfield, and keeps zooming out, and then zooms out of America etc. Keep your eye on the location on the globe where the zoom comes out from and mark it on a screenshot - then compare the screenshot to a same size scaled screenshot of the map using Virtual Earth.
The look on the Virtual Earth map in the exact same location and zoom IN........and guess what......it zooms straight into Springfield.........
and which state?
For those who DON'T want to know.......stop reading now.