IT was an Irishwoman named Catherine O'Leary, and her cow, that were identified as the culprits.
There were claims she was in her barn milking the animal, that a lamp was knocked over, starting the blaze that destroyed over three square miles, killing more than 300 people and leaving 100,000 homeless.
It was untrue, and descendants of Mrs O'Leary believe the lie was driven by anti-Irish sentiment, sometimes rabid, and led by the Chicago Tribune. The allegation stuck and followed the family down the generations.
But while Mrs O'Leary was entirely innocent - and received an official pardon from the city in 1997 - it can be revealed that the actual culprit almost certainly was a recently arrived Irishman, who after the fire fled back home.
Compelling, and detailed, testimony from a witness, rarely published, identifies Denny Connors as the person who accidentally started the fire in October 1871. The recently published Tales of Forgotten Chicago also names Connors.
Mary Callahan, in a 1903 interview, said she was at a party at Pat McLoughlin's, a neighbour. A few decided to go to the barn for milk to make oyster soup. Among them was Denny Connors, Mary said.
"The lamp had been put down on an old milking stool and we were standing by laughing at Denny trying to grip the cow which kept moving away from the strange hands and awkward movements.
"In the dim light, I'll never know whether the cow kicked or Denny fell over the stool in his wild stumbling, but the lamp went over, sure it did, and Alice and myself screamed and ran to the house."
Those in the group scattered, many leaving Chicago as investigations began. "Denny Connors left the city too, and a little later went to Ireland, where he died years ago," she said.
It is a story Mrs O'Leary's great, great granddaughter Peggy Knight was told by her grandmother; that there was a party at a neighbour's house and that a group of young ones were in the barn, though without the detail and no names mentioned.
She was surprised to hear the name of Denny Connors when told by this reporter.
But the lie about Mrs O'Leary was already half way around the world before the last embers died, and the family was ruined.
Reporters went after Mrs O'Leary, variously claiming she was milking the cow at 9pm at night, that she was drunk and, for good measure, was an 80-year-old Irish "hag".
"She was exonerated two days after the fire - but the story stuck," says Peggy. "There were claims that it was for insurance reasons, which was ridiculous, and suspicion because their house was the only one left standing."
Peggy adds: "She was targetted, 100 per cent because she was Irish, called an old hag, even an 80-year-old when she was a hard working mother of five in her forties."
Patrick and Catherine O'Leary bought the lot on the then heavily Irish southside of the city for $500 seven years before the fire. They had five cows and were the sole suppliers of milk in the near neighbourhood.
The couple, Patrick from Kerry, Catherine from Cork, had met in Ireland, but emigrated during the Great Hunger, Peggy believes with two children.
Over the years, and generations, Mrs O'Leary, and her cow, continued to be blamed, casting what Peggy describes as a "dark shadow" across the family, to the point her own grandmother could hardly speak about the matter.
Decades later Peggy's people pelted with potatoes a reporter from the Chicago Tribune, the publication largely blamed for seeding the lie and more broadly feeding anti-Irish sentiment.
"My father, who died in 2015, would never have the Tribune in the house while he lived," says Peggy, whose mother Bridget Walsh emigrated from Ireland as a 12-year-old in the 30s from Farmers Bridge outside Tralee
Peggy, along with her cousins, including Nancy Knight Connolly, a librarian, launched a campaign for an official exoneration, belatedly delivered in 1997 by the City Council and Mayor Richard M. Daley .
Mrs O'Leary died in 1895, her husband a year earlier. The family history is pockmarked with tragedy, including the early deaths of some of the children. But among the survivors were young Catherine, Peggy and Nancy's great grandmother, and Big Jim O'Leary, an infamous tavern owner and illegal bookmaker.
He was still operating in the booze and bookie businesses during the prohibition era but managed to survive the blood soaked turf wars of that Al Capone-dominated era. He died naturally at 56.
Peggy's great great grandfather, James Ledwell, worked for Big Jim for a time before moving in to the more sedate business of seed selling.
Chicago survived and thrived following the fire. Many of the descendants of Catherine and Patrick also thrived, with their people scattered now across Chicagoland and well beyond.
