The Great Fire of Chicago occurred from October 8 to October 10, 1871, devastating a large portion of the city. The fire started in a barn owned by the O'Leary family and quickly spread due to strong winds and wooden buildings. It destroyed over 3 square miles of the city, leaving around 100,000 residents homeless. In the aftermath, the fire claimed approximately 300 lives and caused an estimated $200 million in damages. The disaster led to significant changes in building codes and fire safety regulations, ultimately shaping the future development of Chicago and improving urban fire prevention measures.