According to show creator Matt Groening, it is apparently Springfield, Oregon.
The location of the fictionalized town was revealed by Groening in a recent interview with Smithsonian magazine. In the interview, the 58-year-old recounted that he had named the town after the TV show “Father Knows Best,” which took place in a town called Springfield.
A place where Groening thought was near where he grew up in Portland, Oregon.
“When I grew up, I realized it was just a fictitious name. I also figured out that Springfield was one of the most common names for a city in the U.S. In anticipation of the success of the show, I thought, ‘This will be cool; everyone will think it’s their Springfield.’ And they do.”
When asked why he never spoke of the real town before, he explained, “I don’t want to ruin it for people, you know? Whenever people say it’s Springfield, Ohio, or Springfield, Massachusetts, or Springfield, wherever, I always go, ‘Yup, that’s right.’”