CPD and CFD responded just before 2:30 a.m. to the 3600-block of North Kedvale Avenue for a reported fire in a two-story building there.
The two bodies were found on the first floor of the building after Chicago firefighters had extinguished the blaze.
Chicago fire officials said a mother and son living in the building didn't have any heat for many months and were using space heaters to stay warm.
They also didn't have any working smoke detectors, CFD said.
"It's very upsetting, very sad," said neighbor John Reagan. "We got woken up in the middle fo the night with red lights flashing."
Three other residents in other units in the building were able to get out safely, officials said.
Chicago fire officials canvassed the neighborhood at 10 a.m., providing smoke alarms and safety materials.
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The mother and son were longtime residents in the building and were well-known on the block. The Cook County Medical Examiner identified the two victims as 88-year-old Marian Frieri and her son 70-year-old, Michael Frieri.
"Seemed like a quiet nice guy. Always kept the sidewalks clear -- They were good neighbors. We're gonna miss em," Reagan added.
A neighbor left flowers in the snow in front of the house as the community mourns the loss.
"No one deserves to go out like that. Just terrible what happened here," said fellow neighbor, Alejandra Torres.
CFD said the home was overfilled with possessions and was hard to get around in. Frozen fire hydrants also complicated matters while they tried to fight the fire.
Investigators are still working to determine an exact cause for the blaze, but officials said it was "most probably careless use of smoking materials," officials said.
Cause of fire in 3600 block of N Kedvale is most probably careless use of smocking materials per CFD Office of Fire Investigation. 7— Chicago Fire Media (@CFDMedia) February 8, 2022
Chicago fire officials said their initial investigation shows smoking materials might have started it.
If you're having trouble paying for heat and other utilities, there are financial assistance programs available through the state and other agencies.
Many can be found on the Citizen Utility Board's website, CUBHelpCenter.com.
The state of Illinois also provides the "Low Income Home Energy Assistance Program," which helps eligible low-income households pay for home energy services. Get more information at Illinois.gov/DCEO.