Ruthie is the narrator and protagonist who is profoundly shaped by early childhood abandonment. Left at her grandmother's house by her mother, Ruthie harbors a deep fear of loneliness and being forsaken by adult figures. As she matures, she increasingly mirrors her aunt's transient, unconventional lifestyle rather than conforming to the societal norms of her peers.

Ruthie's younger sister and constant childhood companion. Initially sharing Ruthie's fear of abandonment, Lucille gradually separates from her sister by craving a conventional, orderly life. She becomes increasingly disturbed by their aunt's erratic housekeeping, ultimately taking active steps to secure a standard domestic environment for herself.

The youngest of the Foster sisters, Sylvie is an eccentric, transient aunt who returns to Fingerbone to raise Ruthie and Lucille. She possesses an innate wanderlust and an unusual approach to housekeeping, allowing nature, clutter, and wildlife to overtake the physical house. Despite her roaming spirit, she makes a profound sacrifice by committing to stay in one place to raise her nieces.

The middle Foster daughter and mother to Ruthie and Lucille. Struggling with severe mental health challenges and apathy, she entrusts her children's daytime care to a friend before permanently returning them to her own mother. Her subsequent death by suicide in the local lake leaves a lasting psychological void in her daughters' lives.

The matriarch of the family and widow of Edmund. Sylvia is a highly traditional housekeeper who provides a stable, loving environment for her daughters, though they all eventually leave her. After her middle daughter's death, she diligently raises her granddaughters until her own passing.

The patriarch of the Foster family who leaves his subterranean home to satisfy a deep urge to see the mountains. He builds the family home in Fingerbone before perishing in a catastrophic train derailment. His early wanderlust establishes a thematic precedent for the generations of women in his family.

The eldest daughter of Edmund and Sylvia Foster. She becomes intensely religious during her teenage years and eventually leaves Fingerbone to work as a missionary in China, cutting physical ties with her hometown entirely.

One of Sylvia Foster's elderly sisters-in-law. Accustomed to a comfortable, highly stable life in a Spokane hotel, she travels to Fingerbone to assume guardianship of Ruthie and Lucille but finds the rural house frightening and the responsibility of childcare utterly overwhelming.

Another of Sylvia Foster's elderly sisters-in-law. Finding herself entirely unsuited to raising active children and terrified that the Fingerbone house might collapse during a storm, she and Lily quickly arrange for Sylvie to take over the girls' guardianship.

A highly dedicated friend to Helen Stone who works night shifts and sacrifices her daytime sleep to watch Ruthie and Lucille. She lends Helen her car, which Helen subsequently drives into the lake during her suicide.

The local home-economics teacher in Fingerbone. Representing the complete epitome of domestic order and societal convention, she acts as the community figure Lucille turns to when she desires a stable, traditional home environment.

Ruthie and Lucille's father, who sells farm equipment and is largely absent from their lives. He becomes estranged from Helen early on and completely disappears from the family dynamic after taking up with a cocktail waitress.

The school principal who confronts the Stone sisters about their extensively missed schoolwork. He perceives Ruthie's lack of practical concern as a strict attitude problem and challenges her to speak for herself instead of relying entirely on Lucille.

A classmate of the Stone sisters. Her mother reliably takes her to ballet lessons, presenting an image of the traditional mother-child bond that Lucille acutely desires for herself.