Monday morning, police said Surah Amon, 31, of Chicago has been charged with two counts of murder.
Police said they rushed to the 7000-block of S. South Shore Drive on Friday at about 9:45 p.m.
Investigators said a 31-year-old woman was in the water when they arrived.
They later learned the woman allegedly drowned the boy. Chicago Fire's Marine Unit recovered the boy.
The infant was rushed to Comer Children's Hospital where he died.
According to court documents, she told police she wanted to die.
"Three hours before this happened, me and my sister made a call to the police to have a mental health team come out for my sister," said Claudia Amon, Surah's sister."When the police showed up, they told us there was nothing they could do because my sister was not being violent towards them."
The suspect is on suicide watch, according to court documents.
Amon is due in court again on Tuesday.