The discovery was made near the intersection of 69th Street and Patterson Avenue in Upper Darby Township.
Authorities say the dead infant was found by two people on their way to the store.
"Two witnesses told us that they were walking down here to go to the store and they saw what they believed was an infant. Detectives have arrived on scene and it is confirmed that it is the body of a newborn," said Superintendent Timothy Bernhardt with the Upper Darby Police Department.
Upper Darby residents were sickened by the news on Thursday night.
"That is the most disgusting thing I've ever seen in my life. It's sick, and it breaks my heart because I'm a mom," said Jessica Staten.
Police are still working to determine who may have dumped the child.
Under Pennsylvania's Safe Haven law, you may bring your newborn (up to 28 days old) to any Pennsylvania hospital or law enforcement as long as the baby is unharmed, and not a victim of any crime. You will not be in trouble.
The child has not been identified at this time.
Anyone with any information is asked to call Upper Darby Township police.