Will is a careful, cautious thirteen-year-old boy with white-blond hair, born one minute before midnight on October 30. He is highly protective of those he loves, particularly his best friend Jim and his father Charles. Will acts as the moral center of the story, relying on reflection and thought before rushing into dangerous situations. He is deeply unsettled by the arrival of the Pandemonium Shadow Show and senses the malevolent intentions behind the attractions.

Jim is Will's next-door neighbor, born one minute after midnight on Halloween. He has wild dark hair and a restless, thrill-seeking personality that directly contrasts with Will's caution. Raised by a single mother whose protectiveness makes him feel stifled, Jim is impatient to acquire the independence of adulthood. This longing makes him highly susceptible to the carnival's dark promises.

Charles is Will's fifty-four-year-old father, employed as a janitor at the town library. He feels an acute sense of aging and frequently reflects on the passage of time, wishing he were young enough to run alongside the boys. Despite his physical limitations and self-doubt, Charles possesses a deep love of literature and a philosophical mind that proves vital when investigating the supernatural threat facing Green Town.

Mr. Dark is the sinister co-owner of the Pandemonium Shadow Show, known to the town as the Illustrated Man. His body is covered entirely in supernatural, moving tattoos representing the victims he has trapped through magical bargains. He wields intense psychological control over his followers and preys upon the desires of the townspeople, showing a particular interest in corrupting Jim Nightshade.

A large, red-headed man, Mr. Cooger operates the Pandemonium Shadow Show alongside Mr. Dark. He utilizes the carnival's magical carousel to manipulate his physical age, adopting different identities to deceive the citizens of Green Town. He acts as the brutal physical enforcer to Mr. Dark's psychological manipulation.

Miss Foley is a middle-aged school teacher who taught Will and Jim. She carries a heavy sadness regarding her lost youth and is deeply disturbed after entering the carnival's Mirror Maze, which reflects a younger version of herself. Her desperation to reclaim her past makes her a prime target for the manipulative carnival operators.

The Dust Witch is a blind member of the carnival's troupe who possesses formidable supernatural senses. She flies in a hot air balloon to scout for Mr. Dark, feeling and smelling the emotional states of those she tracks. She acts as an aerial hunter, marking the homes of the carnival's targets to direct the ground forces.

Tom Fury is an itinerant lightning rod salesman who arrives in Green Town warning of a terrible, approaching storm. He gifts a free lightning rod to Will and Jim to protect Jim's house. As he wanders the empty streets at night, he is captivated by a mysterious block of ice at the carnival grounds, illustrating the town's vulnerability to the show's dark allure.

Mrs. Halloway is a calming, stable presence in her home. She represents the quiet comfort of domestic life and provides a safe harbor for her family against the supernatural chaos threatening the town. Charles considers their marriage a combination of halves that created a wholly good son.

Mrs. Nightshade is a single parent who worries constantly about her son growing up too fast. Her intense fear of losing Jim inadvertently makes him feel smothered, driving his desire to break free and age quickly to escape her overprotective hovering.

Mr. Crosetti is the local barber in Green Town. He exhibits strange emotional behavior on the night the carnival arrives, sensing its approach through nostalgic scents on the wind. His shop later displays an illness sign, prompting Will to realize the carnival's sinister impact on the townspeople.

Mr. Tetley owns the cigar store in Green Town. Like other adults in the community, he acts out of character and senses an unnatural tension in the air immediately preceding the arrival of the Pandemonium Shadow Show.