Springfield, Missouri is located in the southwest corner of the state, about a half-hour north of Branson, and is the county seat of Greene County. Founded by Jonathan Polk-Campbell in the middle of the 19th century, it was held by both the Union and the Confederacy during the Civil War. Today, it is the home to Bass Pro, the world's largest outdoor-activity store and museum (and a major tourist attraction) and several colleges including Southwest Missouri State University and Drury College.
There are actually several cities named Springfield in the United States, which may be why The Simpsons is set in a place by that name. (A city called Springfield is also featured in a two-part episode of G.I. Joe, called "There's No Place Like Springfield".)