Corie A. Walsh, 38, was charged in the incident, police said.
Just after 4 p.m. Tuesday, Frankfort police responded to the 22700-block of Brook Stone Court for a report of an unresponsive child.
A 2-year-old boy was taken to a local hospital, where he later died, police said.
Walsh was also taken to a local hospital with non-life threatening injuries.
Police previously said the child's mother was found attempting to hurt herself.
Three other children were also at the home unharmed, police said.
Walsh is currently in custody and being held for medical treatment, police said.
She will be transferred to Will County Jail.
"Our thoughts and prayers are with the family, their loved ones, and everyone affected by this heartbreaking tragedy," police said in a statement.
The Will County Coroner's Office performed an autopsy on the child Wednesday. Final cause and manner of death are pending.
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