Pomona police officers responded to a 911 call about a baby not breathing at 1260 W. 8th Street in Pomona just before 9 a.m. Monday.
The L.A. County Fire dispatcher gave assistance over the phone in starting CPR efforts, according to police. Pomona officers arrived within two minutes of the call and also administered CPR.
L.A. County Fire personnel arrived on scene a short time later and took over CPR efforts.
The child was pronounced dead at the scene.
Police said there were no signs of foul play and there were no suspicious circumstances.
The Coroner's Office and the Pomona Police Detective Bureau were investigating the death. Anyone with information related to the case is asked to call the Detective Bureau at (909) 620-2085. Anonymous callers can contact Crime Stoppers at (800) 222-8477.