Darger was born on April 12, 1892 in Chicago, Illinois, to Henry Darger Sr. and Rosa Fullman. Cook County records show he was born at home, located at 350 W. 24th Street. When he was four years old, his mother died of puerperal fever after giving birth to a daughter, who was given up for adoption; Darger never knew his sister. One of his biographers, the art historian and psychologist John M. MacGregor, discovered that Rosa had two children before Henry, but did not discover their whereabouts.