Mayor Daley urged people to attend the celebration.
It will begin with a torch run at Daley Plaza, followed by a day of family activities at Soldier Field.
The Kennedy family provided funding for the first games. A family member called it the greatest Olympic event ever.
"More than any other games, they fulfilled the greatest Olympic ideal. The Special Olympics taught us of equality, freedom and respect and love of competition and the notion of the athlete as a hero," said Chris Kennedy, nephew of Special Olympics founder.
Chicagoan Mark Affetto was also at Wednesday's event. He participated in the first Special Olympics in 1968. And he remains involved in the games.