Police said they responded at about 10:16 p.m. to the 3500-block of West Lyndale Street for a well-being check.
Officers then found the bodies of a 40-year-old man and a six-year-old boy and police said it appeared the bodies were in a advanced state of decomposition.
They have been identified to the Cook County Medical Examiner's Office as 40-year-old Josean Cano and six-year-old Samuel Cano.
A neighbor who lives in the apartment below said they have not seen the family in weeks.
Area Five detectives are investigating the incident as a death investigation.
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Further details were not immediately available.