The Chicago Fire Department was called to the 3700-block of West 13th Street around 3:30 p.m. where the baby was found in the car seat wearing a snowsuit.
The infant was taken to Mt. Sinai Hospital where she was pronounced dead.
It is unclear where the car seat was found.
Chicago police say two other children, ages 2 and 6, were taken from the home and transported to Mt. Sinai to be checked out. All of the children, girls, were found home alone, police said.
The baby's cause of death was not yet known. The CFD's Larry Langford said the death was "domestic," not cold related.