According to The Hollywood Reporter, The United States of Tara is a single-camera comedy starring Toni Collette as Tara, a wife and mother with dissociative identity disorder.
Larson will play Tara's smart, confident 17-year-old daughter Kate, who struggles with her mother's disorder while rebelling against the world with her own issues. The role was played in the pilot by Portia Doubleday.
John Corbett co-stars as Tara's husband and Kate's father.
Showtime recently picked up The United States of Tara from DreamWorks TV and Steven Spielberg, with a 12-episode order.
Production is slated to begin during the summer in Los Angeles.