According to the Office of the Secretary of State for Illinois, children should stay in the back seat until they are at least 12 years old. Children should remain in a booster seat until they are tall enough to correctly fit in an adult safety belt.
The Office of the Secretary of State says that a belt-positioning booster seat is needed until a lap belt lies low across the child's upper thighs and the shoulder belt fits snugly across his shoulder and chest, not his face or neck. A child may ride in the back seat while wearing only a lap belt if the vehicle does not have a combination lap and shoulder belt and only if the child weighs more than 40 pounds.
