I have to say the miles. The championship circuit went through Springfield from 34 through 71. Races have been at the fairgrounds since 1908. Not only open wheel cars either. ARCA and the USAC stock car divisions have been regulars at the fair. The AMA flat trackers come through Springfield twice a year. I know Indy, DuQuoin, Sacremento, and other miles have extensive histories too, I'm just not as familiar with them.