Catherine O’Leary (née Donegan), was an Irish immigrant living in Chicago, Illinois, dies in Chicago on July 3, 1895. She becomes associated with the origin of the Great Chicago Fire in 1871. She is widely accused of starting the fire when a cow in her barn allegedly kicks over a lantern, though the story is later shown to be unfounded.

Donegan is born in Ireland in March 1827, with more specific accounts placing her birth near Cork, in the Munster province, later emigrating to the United States. She marries Patrick O’Leary, and the couple has three children. Their son, James Patrick O’Leary, later operates a saloon and gambling establishment in Chicago.

On the evening of October 8, 1871, a fire begins in the O’Leary family’s barn on DeKoven Street. Fueled by dry conditions and strong winds, the fire spreads rapidly and destroys a large portion of Chicago.

Shortly after the fire, journalist Michael Ahern publishes a story claiming that the fire had started when a cow kicked over a lantern while it was being milked. Although he does not initially name Catherine O’Leary, she soon becomes associated with the incident because the fire began on her property. The story gains widespread attention and is reinforced by illustrations and caricatures.

In 1893, Ahern admits that he had fabricated the story. The official investigation into the fire concludes that its exact cause could not be determined. Anti-Irish sentiment at the time contributes to the O’Leary family being treated as scapegoats, and various unverified claims circulate about the circumstances of the fire.

O’Leary continues to live in Chicago after the fire. She dies of pneumonia on July 3, 1895, and is buried at Mount Olivet Cemetery.

The story of O’Leary’s cow becomes a widely repeated explanation for the Great Chicago Fire, despite its lack of evidence. In 1997, the Chicago City Council formally exonerates O’Leary of any responsibility for the fire, following research by historian Richard Bales.

O’Leary’s story is dramatized in the film In Old Chicago (1938), in which she is portrayed by Alice Brady, who wins the Academy Award for Best Supporting Actress.