A Springfield teenager formally charged with the premeditated murder of his adoptive mother, whom he stabbed to death early Saturday morning in north Springfield, pleaded not guilty in Sangamon County court Monday.

Jonathan Long, 16, appeared in court wearing a white jumpsuit and handcuffed, sitting next to John Dixon, Sangamon County's assistant public defender.

Long was also charged with aggravated domestic violence.

More:16-year-old arrested after fatal knife attack on his mother in Springfield

Under Illinois law, upon reaching age 16, certain charges, including first-degree murder, automatically result in transfer to adult court.

At Monday's court hearing, Sangamon County Assistant District Attorney Kendra Hansel alleged that Long stabbed 51-year-old Misty Long more than 100 times in the face, neck, stomach, arms and legs.