Todd is a 12-year-old boy living in Prentisstown, thirty days away from his thirteenth birthday, which officially makes him a man. He is the youngest person and only boy in a settlement of 146 men, constantly surrounded by the overwhelming telepathic "Noise" that broadcasts every male's thoughts. Illiterate and self-conscious, he struggles with the aggressive expectations of his town while taking comfort in his dog and the isolation of the swamps.

Viola is a 13-year-old settler from a newly arrived Old World scouting ship. Her appearance heavily shocks Todd, as Prentisstown lore insists all women died from a planetary germ. Having grown up outside the telepathic virus, she projects a complete mental silence that makes her an anomaly in Todd's chaotic environment. She possesses quick wits, strong technical skills, and a practical survival instinct.

Aaron is the intense preacher of Prentisstown whose mind broadcasts a chaotic mixture of violent imagery and religious sermons. He preaches a harsh doctrine and views the passage into manhood as a strict transition from innocence to sin. When Todd discovers a secret in the swamp, Aaron begins tracking the boy with threatening, fanatical motives.

Manchee is Todd's talking dog, a casualty of the planetary phenomenon that gives animals a voice. He communicates his basic needs, like hunger and biological functions, in simple and repetitive vocal bursts. He is fiercely loyal to his owner and serves as Todd's uncomplicated companion in a highly deceptive world.

Ben is one of Todd's guardians and serves as an adopted father. He is unusually kind for a man from Prentisstown and works carefully to shield Todd from the settlement's darker realities. Having trained Todd in survival techniques, he makes urgent preparations to smuggle the boy out of town when dangerous secrets are revealed.

Mayor Prentiss operates as the highly disciplined and manipulative leader of Prentisstown. He maintains strict control over his settlement by banning books and forcing his men to practice mental exercises to structure their chaotic thoughts. He takes an intense, authoritarian interest in Todd's impending birthday and the boy's role in the town's future.

Cillian is Todd's other guardian, sharing a sheep farm with Ben and acting as a surrogate parent. He is more gruff than Ben but equally dedicated to Todd's safety. He aggressively defends the farm and executes a sudden, desperate distraction plan to help Todd escape Prentisstown.

Davy is the teenage son of the Mayor and acts as the sheriff of Prentisstown. Only a few years older than Todd, he uses his position to act as an entitled bully. He eagerly participates in the town's harsh culture and enforces his father's will with violence and intimidation.

Mathilde, who goes by Hildy, is an older woman and resident of the Farbranch settlement. Her existence surprises Todd, who has been raised to believe women are extinct. She demonstrates authority and cautious hospitality when dealing with displaced travelers crossing the river.

Tam is an older man married to Hildy in the Farbranch settlement. He projects his Noise openly and frequently expresses a sense of shared hardship with Todd. He provides early information to the travelers about the history and current state of the New World.

Francia is Hildy's sister and the deputy mayor of Farbranch. She is practical and highly cautious about harboring fugitives who might bring danger to her community. Despite her reservations, she provides temporary shelter while her town votes on the newcomers' fate.

Matthew is a volatile resident of Farbranch whose mind is filled with frightening imagery. He harbors deep animosity toward anyone from Prentisstown. He takes immediate aggressive action against Todd to protect his settlement upon the boy's arrival.

Wilf is an observant man who travels between settlements on a cart. He is kind enough to offer transport to strangers crossing through a herd of local animals. He easily sees through poor attempts at disguise and works to warn others about impending threats to the region.

Jane is a woman traveling in a caravan toward Haven. She is helpful with medical treatment but extremely wary of outsiders. She quickly recognizes the danger associated with anyone hailing from Prentisstown and warns others to keep their distance.

Jessica is Todd's mother, who died before he could form memories of her. She leaves behind a handwritten journal documenting the early days of the New World settlement. Her writings capture the original, optimistic hopes of the colonists and provide Todd with a vital connection to his past.

Dr. Snow is a medical practitioner in Carbonel Downs who provides critical care to a feverish Todd. He operates in a highly defensive settlement that uses blaring loudspeakers to mask private thoughts from outsiders.

Jacob is the young son of Dr. Snow. His mere presence amazes Todd. Having grown up as the youngest resident of Prentisstown, Todd has never seen a young child before arriving in Carbonel Downs.