My theory for Springfield's state
Despite the fact that the Simpsons hometown has been declared as the city without a state, and Springfield USA, but it is still fun to try and figure out what state they may be in.
There is a Springfield in Colorado, Idaho, Illinois, Kentucky, Louisiana, Massachusetts, Missouri, Nebraska, Ohio, Oregon, Pennsylvania, South Carolina, Tennessee, and Vermont. And there is a Shelbyville, Springfield's neiboring and rival town, has a Illinois, Indiana, Kentucky, Tennessee. So that means that The Simpsons are living in either Illinois, Kentucky, or Tennessee.
In "Bart vs. Lisa vs. 3rd Grade", The Capitol City Goofball says, "Mr. Speaker, the time has come to redesign our state flag, this confederate symbol is an embarassment. Particularely as we are a northern state." So that means that they were not a confederate state. Tennessee was a confederate state, so it could not be in Tennessee. So that narrows it down to Springfield being in Kentucky or Illinois.