The donated propane tank caught fire and then exploded at the tent city, which is located on state-owned land at Roosevelt Road and Des Plaines Street near the Dan Ryan Expressway.
The propane tank - one of between 150 and 200 propane cylinders at the encampment - was too close to a space heater.
"This is extremely unsafe," said Major David Byrd, the Illinois State Police Region commander.
On Wednesday, temperatures in Chicago dropped to dangerous, subzero levels. To help the homeless, several people dropped off donated propane tanks to help.
However, the Chicago Fire Department tweeted a warning against donating propane tanks due to the danger.
During extreme cold weather, we understand that people want to help our homeless population. However, we ask that under no circumstance should you donate propane tanks which are potential fire hazards. Propane tanks can cause potential fires and explosions.— Chicago Fire Media (@CFDMedia) January 30, 2019
No one was injured in the explosion.
Donald Gorobegko, who was one of those evicted from the tent city, said he heard a boom, felt the ground shake and then saw smoke.
After the explosion, the area was completely closed off. It was immediately unknown when the residents would be able to return and get their belongings.
The homeless people were moved to shelters, warming centers and hotels.