The Cook County medical examiner says the baby was found dead Sunday night at an apartment complex in Country Club Hills. The baby was pronounced dead at Advocate South Suburban Hospital in nearby Hazel Crest.
An autopsy was inconclusive.
DCFS is investigating an allegation of abuse against the mother, who is said to be 13 years old.
It was unclear whether she suffered a miscarriage or whether foul play was invovled in the death.
(The Associated Press contributed to this report.)