It happened near Avalon and Lindsey on Monday evening.
Investigators say the car left the road and stopped on the frozen water before it broke through the ice. A woman was trapped inside and another woman tried to save her.
The driver's relatives say they're grateful to the Good Samaritan.
"It was an angel for her tonight to save her from water, you know," said Flora Jano, driver's relative.
Officials said the women were transported to Adventist Bolingbrook Hospital and are in stable condition and being treated for hypothermia.
The incident is under investigation.