The Great Chicago Fire was a conflagration that burned in the American city of Chicago, Illinois during October 8–10, 1871. The fire killed approximately 300 people, destroyed roughly 3.3 square miles of the city, including over 17,000 structures, and left more than 100,000 residents homeless. Help flowed to the city from near and far after the fire. The city government improved building codes to stop the rapid spread of future fires and rebuilt rapidly to those higher standards.

Source: Wikipedia