In 1937, a film called "In Old Chicago" was distributed by 20th Century Fox. It tells the story of the Great Fire of 1871.
The film's back story - about the O'Leary family - is fictional. For example:
Despite the movie's fictional back story, historians have praised the film for its depiction of the Great Fire.
NOTE: To see the story of the fire - which, in this film, uses the legend of Mrs. O'Leary and her cow as the ignition source - move the video forward to 09:44.
Clip from "In Old Chicago," a 1937 film, by 20th Century Fox. Copyright, 20th Century Fox, all rights reserved. Clip provided here as fair use for educational purposes and to acquaint new viewers with the production.