According to legend, what was the origin of the Great Chicago Fire?

The Great Chicago Fire, which burned from October 8-10, 1871, destroyed 3.3 square miles of the city, killed around 300 people, and left 100,000 people homeless. The fire originated in or around a barn owned by Patrick and Catherine O'Leary; according to legend, the fire started in the barn when a cow Catherine O'Leary was milking kicked over a lantern. This story has been disproven, and the actual cause of the fire remains unknown. The fire spread quickly due to drought conditions and strong winds, and the city's primarily wooden buildings and sidewalks burned readily.

Source: Massasoit Community College