The baby was found stabbed to death in a motel in the Chicago's Lincoln Square neighborhood.
The mother, Kimberlynn Bolanos, 21, of the 2700 block of W. Balmoral Ave., has been charged with one count of first degree murder.
The child and his mother were found in a first floor room at the Diplomat Motel in the 5200 block of North Lincoln around 10:30 a.m. Thursday morning, according to police.
Motel guest Ernest Randall was in the parking lot taking some items out of his vehicle when he says he saw a man run from the room next to his and into the street where he flagged down a passing squad on patrol.
"The man came running out of the room and said, 'She killed my baby,'" said Randall.
An employee at the Lincoln Avenue motel then called 911.
Officers found the baby dead in the bathroom of the room where the child, his mother, and a man are thought to have stayed since Tuesday.
Police believe the woman stabbed the baby- then herself. She remains in an area hospital.