Los Angeles County sheriff's homicide investigators said the infant was found in the 1300 block of West 105th Street in an incorporated area.
Deputies said they responded to a 911 call Sunday afternoon about a baby not breathing.
"When paramedics arrived on scene, they found a female 1-year-old that was not breathing, and she was pronounced dead here at the scene," said Lt. Holly Francisco of the Los Angeles County Sheriff's Department.
Investigators did not release details. A coroner is investigating the cause of death.
Anyone with information was asked to contact the Los Angeles County Sheriff's Department's Homicide Bureau at (323) 890-5500.