The infant was found wrapped in a shopping bag in a Dumpster behind Moe's Southwest Grill in Granger Saturday night, WSBT-TV, South Bend, reported.
Police said the investigation started when a woman who had just given birth entered the emergency room at St. Joseph Regional Medical Center.
"They had a female who came into the hospital who had just delivered a baby," said Sgt. William Redman with the St. Joseph County Police Department. "However, the baby wasn't present with the mother. Obviously the medical staff there became very concerned."
The woman eventually gave up information that led police to the Dumpster where the baby was found.
Police later searched a home in Granger where investigators suspect the birth occurred. When interviewing neighbors, officers discovered the woman's family was connected to the restaurant where the baby was found.
None of the woman's neighbors knew she was pregnant, police said.
An autopsy of the infant was scheduled.