"Mrs. O'Leary's Cow" refers to a popular legend surrounding the Great Chicago Fire of 1871. According to the story, a cow owned by Mrs. O'Leary kicked over a lantern, igniting the fire that devastated much of Chicago. The blaze lasted for three days, destroying thousands of buildings and leaving many residents homeless. While the tale of the cow is widely known, historians debate its accuracy. Some believe the fire started elsewhere, and the cow's involvement was exaggerated. Regardless, the event led to significant changes in fire safety regulations and urban planning in Chicago.