Comment

Ceez

It IS Missouri. In the episode where Homer starts the security company Springshield, the phone number in the commercial in the show has the area code 636, which is Missouri's.

Parent comment

Robert

It was Springfield Missouri. In the episode where the Simpsons get a sattelite, the beam is coming from the middle of the U.S. so it can't be Massachusettes. And in the news paper, there was a poll on whether the Simpsons were from Illinois or Missouri (Missouri won). So there you have it.