Illinois residents are super excited about the news Six Flags Great America shared about their 50th anniversary. 50th Anniversary Of Six Flags Great America In Illinois. I remember going to Great America the first summer it was opened in 1976. I was super excited to go check it out but I learned quickly the timing wasn’t great. I was too young and little to ride the majority of the rides. It wasn’t the best experience ever but I was ready to come back again down the road.