My first race attended was at the quarter mile dirt oval at Sterling, IL sometime in the mid 1960s. Grandfather took us kids to see one of his friends' son race a 1955 Ford stock car.
First professional races were the USAC dirt champ cars and USAC stock cars on the one mile oval at Springfield IL circa 1970. Foyt, the Unsers, Mario were all regulars on dirt at the time. Quite a lot of history at the track. Wish I'd been there more often.
https://en.wikipedia.org/wiki/Illino...unds_Racetrack
First road race was the CanAm at Road America in 1981.