The Peshtigo fire was a large forest fire on October 8, 1871, in northeastern Wisconsin, United States, including much of the southern half of the Door Peninsula and adjacent parts of the Upper Peninsula of Michigan. The largest community in the affected area was Peshtigo, Wisconsin, which had a population of approximately 1,700 residents. The fire burned about 1.2 million acres (490,000 ha) and is the deadliest wildfire in recorded history, with the number of deaths estimated between 1,500 and 2,500. The exact number of deaths is debated. Data from mass graves, both those already exhumed and those still being discovered, show that the death toll of the blaze was most likely greater than the 1889 Johnstown flood death toll of 2,200 people or more.

Occurring on the same day as the more famous Great Chicago Fire, the Peshtigo fire has been largely forgotten, even though it killed five times as many people.

Nonetheless, several cities in Michigan, including Holland and Manistee (across Lake Michigan from Peshtigo) and Port Huron (at the southern end of Lake Huron), also had major fires on the same day. These fires, along with many other fires of the 19th century had the same basic causes: small fires coupled with unusually dry weather.

Slash-and-burn land management was a common way to clear forest for farming and railroad construction. This allowed for farmers to have good soil for planting but contributed to the fires that burned all summer and into the fall. Due to the benefit of having the controlled fires, many people including immigrants from Europe believed that fire was an ally. On the day of the Peshtigo fire, an eastward-moving cold front increased the wind speed and spread the fires, merging several.

A firestorm ensued. In the words of Gess and Lutz, in a firestorm "superheated flames of at least 2,000 degrees Fahrenheit ... advance on winds of 110 miles per hour or stronger. The diameter of such a fire ranges from one thousand to ten thousand feet ... When a firestorm erupts in a forest, it is a blowup, nature's nuclear explosion ... "

By the time it was over, between 1.2 and 1.5 million acres of land had been burned. In addition to Peshtigo, 16 other communities were destroyed in the fire.

The value of the property and forest that was destroyed in the fire was estimated to be about $5 million US (about $127 million in 2024 dollars). Additionally, 2,000,000 trees, saplings, and animals perished in the fire; this had a devastating economic impact on the area as well.

An accurate death toll has never been determined because all local records were destroyed in the fire. Estimates vary from 1,200 to 2,400 deaths.

The 1873 Report to the Wisconsin Legislature listed 1,182 names of dead or missing residents. In 1870, the Town of Peshtigo had 1,749 residents. More than 350 bodies were buried in a mass grave, primarily because so many people had died that there was no one left alive who could identify them. The Peshtigo Fire Cemetery was entered into the National Register of Historic Places which is determined by age, integrity and significance of the site.

The Rev. Peter Pernin, in his eyewitness account, states that the prolonged drought at that time combined with the factor of human carelessness were omens of the horrible disaster. He also notes how the fire seemed to jump across the Peshtigo River using the bridges and upward air drafts and burn both sides of the town.

Other survivors reported that the firestorm generated a fire whirl (described as a tornado) that threw rail cars and houses into the air. Many citizens escaped the flames by immersing themselves in the Peshtigo River, wells, or other nearby bodies of water. Some drowned while others succumbed to hypothermia in the frigid river. In one account, a man slit the throats of all his children to spare them from an agonizing death.

At the same time, another fire burned parts of the Door Peninsula; because of the coincidence, some incorrectly assumed that the Peshtigo fire had jumped across the waters of Green Bay into the Door County regions. However, the fire did not jump across the bay. Most likely, the firestorm spread and created a new ground fire in New Franken which then spread and burned everything northward up until Sturgeon Bay.

Speculation since 1883 has suggested that the start of the Peshtigo and Chicago fires on the same day was not coincidental, but that all the major fires in Illinois, Michigan and Wisconsin that day were caused by impact of fragments from Biela's Comet. This hypothesis was revived in a 1985 book, reviewed in a 1997 documentary, and investigated in a 2004 paper published by the American Institute of Aeronautics and Astronautics.

Certain behaviors of the Chicago and Peshtigo fires were cited to support the idea of an extraterrestrial cause, such as blue flames (thought to be cometary gases burning) in the basements of houses. However, modern fire theory indicates that the blue color was most likely a product of burning carbon monoxide in the poorly ventilated basements. Additionally, scientists with expertise in the field pointed out that there has never been a credible report of a fire being started by a meteorite.

In any event, no external source of ignition was needed. There were already numerous small fires burning in the area as part of land-clearing operations and similar activities after a tinder-dry summer. All that was necessary to trigger the firestorm, plus the other large fires in the Midwest, was a strong wind from the weather front which had moved in that evening.

The wildfire remains the deadliest in the history of the United States. Following the fire, it took days for help to arrive. By the time that word got to Madison, most of the officials and their aid were going to Chicago, which was being called the Great Fire. Food, clothing, and other aid were quickly sent in order to help survivors, many of whom went to Marinette. All that was left of the Town of Peshtigo were a few buildings and ashes with all personal items being destroyed.

William Butler Ogden, a politician and lumber company owner, went to Peshtigo with the goal of rebuilding the town. It took years to rebuild and many businesses never reopened. Specifically, the large woodenware factory that supplied jobs to many was never rebuilt, leaving the town to never re-establish their lumber industry. Today, Peshtigo is a typical northeastern Wisconsin town, and has roughly 3,500 residents.

The Peshtigo Fire Museum, just west of U.S. Highway 41, has a small collection of fire artifacts, first-person accounts, and a graveyard dedicated to victims of the tragedy. A memorial commemorating the fire was dedicated on October 8, 2012, at the bridge over the Peshtigo River.

The National Shrine of Our Lady of Good Help, a Marian shrine in Champion, was established at the site of a chapel where Sister Adele Brise and others sheltered from the fire and survived. According to Sister Adele, in October 1859, she had a vision of the Blessed Virgin Mary with a warning, saying "If they do not convert and do penance, my Son will be obliged to punish them." Twelve years later, the fire erupted and many people flocked to the church for safety. The people prayed the rosary, and hours later rain came, which put out the fire. Some of the very few things that survived the Peshtigo Fire were the convent, school, and chapel and five acres of land that had been consecrated to the Virgin Mary. The only animals that survived were those that were brought to the chapel grounds. Following the fire, people had great faith in the chapel and the Virgin Mary because they believe that she had saved them. In the following years, it was claimed that miracles occurred at the chapel. In one account, a blind girl went to the chapel to pray and came out able to see; however, none of these stories have ever been reliably documented.

Tornado Memorial County Park is located on the site of the former community of Williamsonville, a small village in Door County, and is named for the fire whirl which occurred there. The park is the only thing left of the small town as the firestorm destroyed everything. Out of the 76 inhabitants of Williamsonville, there were only 19 survivors. As a result of the fire, Williamsonville was wiped off the map as it was never rebuilt.

The combination of topography, geography, wind conditions,and ignition sources that led to the fire is known as the "Peshtigo paradigm". The American and British militaries studied the fire during World War II to learn how to recreate firestorms during bombing campaigns against cities in Germany and Japan. Denise Gess, co-author of Firestorm at Peshtigo, said, "They actually made a 'demo' first, a little scale model of wooden buildings, and studied how you would drop bombs until it created a firestorm. Something that devastating and that hot."

Rutkow (2012) writes that the event prompted almost no change to the practices of the lumber industry or the way settlers approached life in forests. He notes that in the following decades, the rate of industrial logging increased and the amount of forest fires increased throughout the country, with Wisconsin itself experiencing major fires in 1880, 1891, 1894, 1897, 1908, 1910, 1923, 1931, and 1936. The loss of half a million acres a year was not uncommon.

The Peshtigo Fire is discussed in Season 1, Episode 8, of the television series The Gilded Age when downstairs character Jack is discovered putting flowers on the grave of his mother, who died in the tragedy.

• Great Chicago Fire
• Great Michigan Fire
• Port Huron Fire of 1871

• Great Hinckley Fire of 1894
• Baudette fire of 1910
• Cloquet fire of 1918
• Thumb Fire of 1881 (see also List of Michigan wildfires)

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• Bergstrom, Bill (2003). Peshtigo. Philadelphia: Xlibris Corporation. ISBN 978-1401098889.
• Holbrook, Stewart (August 1956). "Fire Makes Wind: Wind Makes Fire". American Heritage. Vol. 7, no. 5.
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• Pernin, Peter (Summer 1971). "The Great Peshtigo Fire: An Eyewitness Account". Wisconsin Magazine of History. Vol. 54, no. 4. pp. 246–272.
• Rutkow, Eric (April 24, 2012). American Canopy: Trees, Forests, and the Making of a Nation. New York: Scribner. pp. 115–120. ISBN 978-1-4391-9354-9.
• "The Great Midwest Wildfires of 1871". NOAA's National Weather Service. April 29, 2022.
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• "The Fire Fiend". The New York Times. October 13, 1871.
• DeLaluzern, Guillaume (October 1871). "IN WISCONSIN. Particulars of the Burning of Williamsonville and Peshtigo – Frightful Number of Deaths". Green Bay Advocate. Archived from the original on May 31, 2013. Retrieved November 20, 2011.
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• "Survivor's stories". Rootsweb.com. Retrieved March 1, 2013.
• Peshtigo Fire at the Wisconsin Historical Society's Dictionary of Wisconsin History
• "Peshtigo fire photos". Wisconsin Historical Society.