Gilbert is a 24-year-old who works at Lamson Grocery in the small town of Endora, Iowa. He serves as a primary caregiver for his younger brother Arnie and helps run a household altered by past tragedy and his mother's severe obesity. Though he feels trapped by his family responsibilities and the stagnation of his small town, his actions reveal a deep loyalty to his loved ones.

Arnie is Gilbert's 17-year-old younger brother, who has an intellectual disability. Nearing his 18th birthday, a milestone doctors predicted he would not reach, he is the center of the Grape family's attention and care. He loves the carnival, particularly the carousel horses, and relies entirely on his siblings for his daily needs.

At 34 years old, Amy is Gilbert's older sister and the primary mother figure of the Grape household. She works as a teacher's aide during the school year and manages the daily tasks of cooking, cleaning, and organizing family events. She puts her own youth and personal life on hold to maintain order and care for her siblings and mother.

Bonnie is the matriarch of the Grape family, permanently confined to the living room chair due to her severe obesity. Once a beautiful young woman with many suitors, she retreated into grief and excessive eating following the suicide of her husband, Albert. Her primary focus is living to see Arnie reach his 18th birthday.

Ellen is Gilbert's 16-year-old sister who works at the local Dairy Dream. She focuses on her appearance, teenage social dynamics, and religion as a social outlet. She frequently clashes with Gilbert and actively avoids taking on household responsibilities.

Tucker is Gilbert's best friend in Endora. He lives in an apartment his parents built in their garage and enthusiastically supports the town's changes, particularly the construction of a new Burger Barn. He assists Gilbert with practical tasks around the Grape house but lives a much simpler, carefree life.

Becky is a 15-year-old girl visiting her grandmother in Endora from Ann Arbor, Michigan. Her arrival disrupts the local social scene, drawing the attention of all the young men in town. She is highly perceptive and emotionally direct, pushing Gilbert to confront his buried feelings.

Mrs. Carver is a married woman living in Endora who projects the image of a perfect family life. Behind closed doors, she is unhappy in her marriage and engages in secret meetings with Gilbert, clinging to him because she believes he will never leave town.

Mr. Carver is a local insurance agent obsessed with outward appearances and maintaining the illusion of a perfect family. He purchases a trampoline to appease his sons when he cannot afford a pool, occasionally displaying aggressive behavior when his family fails to project the image he desires.

Larry is the 32-year-old eldest brother of the Grape family. He lives away from Endora, makes a good living, and sends financial support to the household. He avoids returning to the family home, visiting only once a year for Arnie's birthday.

Janice is the 29-year-old older sister of the Grape family who works as a flight attendant. Armed with a psychology degree, she tends to analyze her family members from a distance. Like Larry, she sends money home but is largely absent from their daily struggles.

Albert is the deceased patriarch of the Grape family. He died of suicide 17 years before the story begins, hanging himself in the basement of the family home. His death remains a defining trauma for the entire family, shaping their present dysfunctions and emotional blockages.

Mr. Lamson is the owner of Lamson Grocery, the older, struggling independent grocery store in Endora. He is optimistic, hard-working, and serves as a vital father figure for Gilbert, even as his business faces the threat of the newly opened Food Land.

Lance is a former classmate of Gilbert's who has achieved minor celebrity status as a television reporter. While the townspeople treat him as a hero, Gilbert remembers him as a childhood tattletale and harbors deep resentment toward him regarding the day of Albert Grape's death.

Melanie is a former library assistant who now works as Mr. Carver's secretary. She attempts to make small talk with Gilbert about his family and is entangled in the dysfunctional, secret dynamics of the Carver business.

Bobby is the son of the local funeral home owner and a friend of Tucker's. He occasionally drives his father's hearse around town and eventually begins dating Ellen Grape.

Mrs. Brainer is Gilbert's second-grade teacher whose recent death brings up painful memories. Her strict classroom rules play a significant role in Gilbert's childhood trauma, as she prevented him from going home to check on his father on the day of his suicide.

Cindy is the manager at Dairy Dream and the owner's daughter. She uses religion as a social outlet and attempts to recruit Gilbert and Ellen into her Bible study group.

Sheriff Farrell is the local law enforcement officer in Endora. He once had romantic feelings for Bonnie after her husband died and is shocked by her physical transformation when she arrives at his office to retrieve Arnie.

Dave owns a local gas station in Endora. Gilbert prefers his station because the arrival bell is broken, reflecting Gilbert's desire for silence and avoidance of attention.