Officers responded to a 911 call reporting that the baby at a Riverhead residence, on 3rd Street, was unconscious and not breathing.
CPR was performed, but the infant was pronounced dead at Peconic Bay Medical Center in Riverhead.
Riverhead Town PD detectives and the Suffolk County Medical Examiner's Office are investigating the circumstances that led to the child's death.
Police said social workers have been made available to assist the family.
This is a developing story. Check back to Daily Voice for updates.
Click here to follow Daily Voice Malverne and receive free news updates.