His family gathered at Harry Caray's restaurant on Navy Pier, joining Cubs great Ernie Banks and the team's owner Tom Ricketts.
The Hall announced its selection on Monday, nearly a year after Santo's death.
The third baseman was a nine-time All Star who hit 342 home runs and won five Gold Gloves
"His dream was that one day I'll be in the hall of fame. He's got me and Billy and Fergie and Sandberg and the rest of us," said Banks.
"He accomplished everything there was. This is the icing on the cake. I'm sorry he's not here but it's just a great honor," said Vicky Santo, Ron's widow.
Santo's widow refused to say the honor was bittersweet and said the important thing is his legacy will continue.