The Great Chicago Fire began in the evening on Oct. 8, 1871. For nearly three days, it burned 3.3 square miles of the city to the ground, leaving 100,000 homeless and more than 300 dead. The fire spread quickly due to dry weather conditions, the close proximity of buildings to one another and the buildings' wooden construction.
The exact cause of the Great Chicago Fire has been debated for over a century, but most accounts agree that it began around 9 p.m. The fire started in a barn or adjacent shed on DeKoven Street that belonged to Catherine O'Leary. Popular legend has it that her cow kicked a lantern over to start the conflagration, but human carelessness is considered by many historians to be a more likely cause.
The fire spread quickly from the O'Leary property, aided by strong southwestern winds. Many of the buildings in old Chicago were built nearly side-by-side, using wooden balloon frame construction. The predominance of wood as a construction material and the extraordinarily dry weather that the city had experienced for more than three months caused the fire to rapidly engulf entire city blocks.
Firefighting efforts were also ineffective. Local departments were exhausted from fighting smaller fires earlier in the week and initially reported to the wrong location. After a few hours, the fire jumped the Chicago River and ignited the city's main water pumping station. It soon became engulfed, cutting off the water supply and leaving firemen helpless to contain the blaze.
The fire finally burned itself out on Monday, October 10, aided by a providential rainstorm the previous night. Today the Chicago Fire Academy stands on the site of the O'Leary property, with a marker commemorating the spot where the disaster began.