Peshtigo was a center of manufacture of wood products of all sorts in 1871, sitting as it did in the center of a large area of timbering. The summer was especially dry, and sporadic fires were breaking out in the surrounding forest. Deliberately-set fires were also used extensively at the time to clear land for planting crops and other development. A railroad line was being constructed from Milwaukee to Michigan's Upper Peninsula, and debris from clearing the path was left to burn by the wayside. In the days before the firestorm broke out smoke from these smaller "controlled" fires was so thick that ships on Green Bay were forced to use their foghorns and navigate by compass.
On the fateful day a cold front moved in from the west, bringing strong winds that fanned the smaller prairie fires and escalated them to Biblical proportions. By the time it was over 1,875 square miles (4,850 km² or 1.2 million acres) of forest were consumed, an area approximately twice the size of the state of Rhode Island. Some sources list 1.5 million acres burned. 12 towns were destroyed. An accurate death toll has never been determined since the local population records were destroyed in the fire, with estimates of between 1,200 and 2,500 people thought to have lost their lives. More than 400 bodies were buried in a mass grave primarily because so many died no one remained alive who could identify the dead. The fire jumped Green Bay and then burned on both sides. Surviving witnesses in Peshtigo reported that the firestorm generated a tornado capable of throwing rail cars and houses into the air. Many of the survivors of the firestorm escaped the flames by hiding in the Peshtigo River or other nearby bodies of water.
The Peshtigo Fire Museum has a good display about this historic event. Their pamphlet is recommended for first-person descriptions about the tragedy and for astonishing accounts of what an uncontrolled firestorm is like from the ground.
Another historical irony--National Fire Protection Week is in October in commemoration of the economic loss of the Chicago fire. Again Peshtigo stands unremembered.
The combination of wind, topography and fire that created the firestorm is known as the Peshtigo Paradigm. The elements that created it were studied and recreated by the American and British military during World War II for the fire bombings of German and Japanese cities.