Guys, NO state fits the Simpson's Springfield anywhere near 50%, much less 100%.
Matt Groening picked the name "Springfield" because it's the first or second most common town name in America. It was created with the intent that they could morph the town into any place they wanted it to be. The minute they gave the town a state, they would have been forced into conforming it to meet the general properties of that state and town.
The state is never mentioned, so that they may morph Springfield into any town and any location they please. They've had Springfield morphed into a hollywood-esque location before, complete with a Springfield sign in the hills, theme shaped restaurants, and a shady celebrity history. The view from the hills above Springfield looks like the view from Mulholland drive in LA. (This makes sense, because the writers are in LA, and write about what they're familer with) They've even jumped on a boat and been in international waters within minutes.
They've had Springfield be a short drive from TN, New York, the ocean, the desert and midwest style corn fields and farms. They've even had Springfield as a port town complete with light houses and piers in a number of episodes. (Including the one with Mr Burn's boat in international waters)
Springfield is the Visa of towns. It's everywhere you want it to be. There is NO WAY you can name a specific state, because the town morphs every week.