Catherine O'Leary (a.k.a. Kate O'Leary) (b. circa 1827, d. 1895) was an Irish immigrant living in Chicago, Illinois in the 1870s. On the evening of October 7, 1871, a fire started in her barn at 137 DeKoven Street which went on to burn a large percentage of the city, an event known as the Great Chicago Fire. She was married to Patrick O'Leary.

Although for many years, it was believed that the fire began with the O'Learys' cow knocked over a lantern, historians now place the blame on Daniel "Pegleg" Sullivan who may have been gambling in the barn with the O'Leary's son, James , who went on to become one of the major gambling hall owners in Chicago in the early twentieth century.