Claudia De La Roca for Smithsonian magazine:

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.

Go ahead and read the interview if you want to know which Springfield inspired him, though.

(Via the Washington Post.)