Jeremy Froemming, 38, told an officer he took three different types of pills Sunday afternoon.
He crashed into trees near Highway 67 and Highway D in the town of Ottawa at about 1:30 a.m.
Both Froemming and his son were trapped inside.
The boy was flown by Flight for Life to Children’s Hospital, where he remains, but doctors were unable to save his arm.
Court documents show Froemming has three prior OWI offense. He is charged with intoxicated use of a vehicle — great bodily harm and operating a motor vehicle while intoxicated — fourth offense, with a minor child in the vehicle.