Streamwood police and paramedics responded to a call from the Salvation Army in the 1000-block of South Barrington Road after the baby was found unresponsive. An autopsy found that he died of strangulation and the death was ruled a homicide.
Police released a sketch of the woman, believed to be the baby's mother. Police say they think the woman gave birth in the bathroom. She may have also entered the store with another woman and child.
Illinois' Safe Haven Law allows parents to give up a child 30-days old or younger at any hospital, police or fire station.
"They can walk away with no questions asked. They won't be prosecuted. Baby is saved. Mom is safe," said Dawn Geras, Save Abandoned Babies Foundation.
The mother is described as being between 5 feet 1 inch to 5 feet 4 inches tall, Hispanic, and between the ages of 14 and 25.
Anyone with information should call Streamwood police.