of two sons of Richard Head Welles and Beatrice Ives Welles (née Beatrice Lucy Ives). He was named after one of his great-grandfathers, Kenosha attorney Orson S. Head, and his brother George Head. Orson's brother, Richard Ives Welles, who was ten years older, struggled with mental health problems and was often institutionalized.

Despite his family's affluence, Welles encountered hardship when his parents separated and moved to Chicago in 1919. His father, who made