Because of child labor laws, Joel Coen and Ethan Coen were unable to film any scenes past midnight with Hailee Steinfeld (especially difficult because the movie contains many night scenes), and because of scheduling problems, any time there is a shot of another character over Mattie's shoulder or back, Mattie is played by an adult double, not Steinfeld.
Despite Mattie Ross having the most screen time and being considered the protagonist, Hailee Steinfeld was nominated for Best Supporting Actress in many award shows, including the Academy Awards.
15,000 girls applied for the role of the young Mattie Ross, the part going to Hailee Steinfeld. She was 13 years old when cast. It was her theatrical feature-film debut.
Jeff Bridges said that the first piece of direction the Coens gave him was to forget about the John Wayne version. Their movie would be a return to the 1968 source material by the original author Charles Portis.
As mentioned in the trivia from the original True Grit (1969), the character of Rooster Cogburn is supposed to be around 40, both John Wayne and Jeff Bridges were in their early 60's when they portrayed their roles. John Wayne was 62, Jeff Bridges was 60.