Theres a metra train that stops about 2 blocks away from the park,
Metra Six Flags Transit
And then theres Pace Bus service
Pace Bus serive To Sfgam
Hope that helps ya, if you live in the far south suburbs, as do I, you can ride the metra train to the randolph station downtown, then take the north line to waukegan, coast about $15-20 depending on the conductor
P.S. I wouldnt recomend Metra until the Taste Of Chicago is over.