On October 8, 1871, flames spark in the Chicago barn of Patrick
and Catherine O’Leary, igniting a two-day blaze that killed
between 200 and 300 people, destroyed 17,450 buildings, left
100,000 homeless and caused an estimated $200 million
(in 1871 dollars; roughly $4 billion in 2021 dollars) in damages.

Legend has it that a cow kicked over a lantern in the O’Leary barn
and started the fire, but other theories hold that humans or even
a comet may have been responsible for the event that left four
square miles of the Windy City, including its business district, in
ruins. Dry weather and an abundance of wooden buildings, streets
and sidewalks made Chicago vulnerable to fire.