Billy the Lonely Boy is character from the film. He is an eight-year-old who thinks Christmas does not work out for him.
Billy lives close by Hero Boy at 11344 Edbrooke Avenue in Grand Rapids, Michigan. Billy's family lives in poverty, as depicted by the film. His house is described as being "on the wrong side of the tracks" to the other children's houses and his appearance is much simpler and poorer than his friends. Billy believes that Christmas does not work out for him because his parents do not have enough money to buy him presents, which is why he is so resistant to part with his gift, as it is his first one and he does not want to lose it. His house is more run down than the other houses in the neighborhood and from outside the window, Billy's Christmas tree is more sparse and smaller than the tree in the house of the Hero Boy. He is reluctant to make friends as he feels intimidated by the others' wealth, and he is afraid of what they will think of him if they realize that his family lives in poverty.
One Christmas Eve, the Polar Express stops in front of Billy's house. Billy initially decides to stay behind, but he runs after the train after changing his mind. He cannot keep up, however, so Hero Boy pulls the emergency brake to stop the train. He gets on and sits in the observation car, away from the other children. When the waiters serve hot chocolate, Hero Girl and the Conductor bring him some after realizing he did not get any, which causes Hero Boy to lose Hero Girl's ticket while trying to bring it to her.
The Conductor must have punched his ticket sometime during the journey, but such a scene in which this happens is never shown. He punches out the word "ON" on the right end of the ticket.
When Hero Boy is trying to return Hero Girl her ticket, he passes by Billy in the observation car and asks where she and the Conductor went, but Billy does not respond. Suddenly, Hero Boy sees their shadow out the window (it was really the Hobo's) and goes to climb onto the train.
Later, Billy meets Hero Boy when he and Hero Girl sing "When Christmas Comes to Town." Afterwards, they all see the Northern Lights form while the Conductor shows up to inform them that the train has crossed the Arctic Circle, then shows them the North Pole in the distance.
When all the other children go to meet Santa, Billy chooses to stay behind, but Hero Girl and Hero Boy decide get back on the train to attempt to convince him to come, but Hero Boy accidentally steps on the coupler cut level, which causes the car to uncouple from the rest of the train and roll down a hill. Once the train stops on a turntable after Hero Boy turns the brake wheel, the three set out to get back to the center of the city. Along the way, they find Billy's Christmas present, which was the last one wrapped. Billy grabs it, leading the other two to follow, where they end up with the rest of the presents in Santa's bag. Billy wants to open his present early, but Hero Girl points out a note on the present saying, "Do not open until Christmas." While the bag is being carried to the center of the North Pole, something in the bag grabs Billy's leg, so Hero Boy and Hero Girl help to pull him free. It turns out to be Know-It-All, who claims he was checking out his presents to make sure he will get everything he wants. When they arrive at the city center, all the children are rescued from the bag by the elves. One elf takes the present from him and puts it back in the bag, assuring him it will be in good hands.
Before Santa announces who will receive the first gift of Christmas, he congratulates Billy for having made new friends, saying that friendship is the best gift of all. Later, Billy's ticket gets punched for the return trip. When he first looks at it, it reads, "DEPEND ON", but it changes to "RELY ON" and "COUNT ON" after each time he flips it. "That is some special ticket," the Conductor remarks.
Before getting dropped off, Know-It-All questions why he is leaving until he explains that he is going home. Billy also thanks Hero Boy for stopping the train for him. After getting back to his house, he comes back out holding his present up and calling out from his front porch to Hero Boy and Hero Girl that Santa has been to his house.
It is never revealed in the film what Billy's present was.
- Billy is one of many characters in the film to not originate from the book.
- Billy is the only passenger on the train, and one of few characters in the film, identified by name.
- In real life, Billy's address, 11344 Edbrooke Avenue, is the address of Robert Zemeckis' childhood home. The home is in the south side of the Chicago neighborhood of Roseland.
- Billy is referred to only as Lonely Boy in the credits.
- "My name is Billy!"
- "That's my address!"
- "I think I know what it is! I wanted one of these my whole life!"
- "Absolutely. Me... and my friends."
- "Thanks for stopping the train for me."
- "Look, look! Santa got here!"