Look at the map. It shows all the states that can not be the State in which the Simpsons live in which are all coloured in red. All the states in white are the remaining ones.
Underneath, there is a table with each state and it explains why each of the red states have been eliminated with proof from quotes from many different episodes.
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Also to add onto that, go on this website: http://www.simpsonsstate.com/
Look at the map. It shows all the states that can not be the State in which the Simpsons live in which are all coloured in red. All the states in white are the remaining ones.
Underneath, there is a table with each state and it explains why each of the red states have been eliminated with proof from quotes from many different episodes.