The Great Chicago Fire of 1871 did indeed start in Mrs. O'Leary's barn
as the poem says. The Fire destroyed 3 square miles of Chicago
and left 100,000 people homeless; but the O'Leary home attached to
the barn wasn't damaged at all. It is believed the fire was caused by
ashes from a pipe a worker had in his mouth,and not Mrs.O'Leary's cow!