Mrs. O'Leary is a figure associated with the Great Chicago Fire of 1871. She was a dairy farmer who lived in Chicago, and her barn was said to be the starting point of the devastating fire that destroyed much of the city. The exact cause of the fire remains uncertain, but the legend of Mrs. O'Leary's cow kicking over a lantern has become a popular story. The Great Chicago Fire lasted from October 8 to October 10, 1871, and resulted in significant loss of life and property. It left over 100,000 people homeless and destroyed approximately 3.3 square miles of the city. The fire led to major changes in building codes and urban planning in Chicago, shaping the city's future development.