Using a state-by-state Mapquest search, you can find 53 Springfields in 34 states. Which real Springfield is the model for the Springfield on The Simpsons? It's hard to say. But there have been clues in various episodes that make some fans sure they know they true location.
Many fans say "Behind the Laughter" definitively noted that Springfield was in Kentucky, per the narrator. But in repeats of that episode, the narrator said Springfield was in Missouri.
In 2012, Matt Groening revealed to the Smithsonian that Father Knows Best was his inspiration, because the show was set in Springfield. As a child, Groening thought they meant his Springfield, near his home in Portland, Oregon.
According to interviews, Matt Groening chose the name "Springfield" simply because it is one of the most common city names in the United States. But Groening and the writers have enjoyed teasing fans with clues as to where the town might be located.