The Great Chicago Fire that destroyed 3.3 square miles of Chicago, Illinois burned for 2 days in 1871 (October 8th - October 10th). It killed hundreds of people, and over 100,000 people were left homeless. It destroyed roughly 17,000 buildings and caused several 100 million of dollars in damage (about $4-$5 billion today).

A popular story about this 1871 Great Chicago Fire has been concerned with how it started. It was reported that a cow in the barn owned by Kate O’Leary ignited the fire. The cow kicked over a lantern. Thereafter, it became the subject of a children’s song:

Late one night, when we were all in bed,

Mrs. O’Leary lit a lantern in the shed.

Her cow kicked it over,

Then winked her eye and said,

“There’ll be a hot time in the old town tonight!”

Now it is hard to know the true facts about how the fire started. The story about the O’Leary cow is false. The guy who wrote the O’Leary story for the Chicago Republican, Michael Ahern, admitted that he made it up. He said that it made for a more interesting story. The fire did start in the vicinity of the O’Leary's barn. But, the exact cause of the fire was never determined. The O’Leary family were used as a scapegoat.

It was also said a thief knocked over a lantern and started the fire. Later, a man named Louis M. Cohn confessed to accidentally starting the fire. He was running away from an illegal card game. Now, scientists have suggested that a meteor shower ignited hay in the O'Leary barn.

More Info: en.wikipedia.org