FactSentinel

The Great Chicago Fire began on the night of October 8, 1871, in or near the O'Leary family barn on DeKoven Street, but the claim that a cow kicked over a lantern and started it has never been supported by reliable evidence. The story is best understood as a durable piece of folklore rather than a documented account of what happened. The 1871 Chicago Board of Police and Fire Commissioners held an inquiry soon after the disaster, and Catherine O'Leary testified that she and her family were in bed when the fire started. The inquiry could not determine the cause, and it did not conclude that a cow was responsible.

The cow story appears to have spread through newspaper coverage in the days after the fire. In 1893, Michael Ahern, the Chicago Republic reporter who helped popularize the tale, admitted that he had invented the cow-and-lantern detail because it made for a vivid story. Historians also note that the O'Learys, as poor Irish Catholic immigrants, were convenient targets for blame amid the anti-immigrant prejudice of the time. In 1997, the Chicago City Council passed a resolution formally exonerating Catherine O'Leary and her cow.

The actual cause remains unknown. Neighbors, including Daniel "Peg Leg" Sullivan, who first reported the blaze, have been suggested as possible sources, and other theories involve stray sparks or even a falling meteor, though none is proven. Dry conditions, wooden buildings, and strong winds explain why the fire spread so destructively, but the original spark is still a mystery.