Judson is a twelve-year-old boy living in Madison, Wisconsin. Known for his average looks and his tendency to treat everything as a joke, he lacks political knowledge but possesses a likable, easygoing personality. He runs for President of the United States as a candidate for the newly formed Lemonade Party. He relies entirely on humor and the direction of his campaign manager.

Lane is Judson's highly intelligent and strategic best friend. Acting as the brains behind the operation, he handles the logistics of the presidential campaign. He organizes press interviews, selects campaign staff, and figures out how to raise campaign funds. He is motivated by a desire to be part of a winning team, stemming from a childhood history of constantly losing games like King of the Hill.

June is an elderly African American woman who uses a wheelchair due to Parkinson's disease. As Judson's former babysitter, she offers him grounded advice and a realistic adult perspective on his antics. She reluctantly agrees to join Judson's ticket as his vice-presidential running mate primarily to keep an eye on him.

Arthur is a knowledgeable and serious student at Judson's school who wears a tie and appreciates homework. He frequently questions Judson's political qualifications. He represents the segment of the population that demands substance over entertainment in political campaigns.

Chelsea is described as the prettiest girl in Judson's school, possessing an outgoing personality and model-like looks. She agrees to serve as Judson's "First Babe" primarily because she enjoys the prospect of attending parties and having her photo taken to boost her modeling career. She later takes up the cause of saving silkworms.

Abby is a genuine, long-time friend of Judson. She believes he would make a good president because he is a real person rather than a phony politician. Her role in Judson's life shifts as the campaign focuses more on cultivating a specific image, pushing her slightly to the periphery.

Pete is a local reporter for the Capital Times in Madison, Wisconsin. Initially skeptical of a twelve-year-old running for president, he becomes the first journalist to cover Judson's story after attending the campaign's lemonade stand launch. He actively looks for newsworthy angles to report on as the campaign grows.

Judson's parents work in sales, with his father selling cardboard boxes and his mother selling carpet tiles. They are often tired from work and initially pay little attention to Judson's campaign. They simply require that he finish his homework and mow the lawn before getting involved in politics, treating his run as a regular childhood phase.

George White is the incumbent President of the United States. His public image recently suffered after an embarrassing televised incident involving his dog. He faces Judson as a political challenger in the upcoming election and participates in a national televised debate.

Senator Dunn from Virginia is a traditional political candidate running for President of the United States. He participates in national debates against President White and Judson, attempting to discuss actual political issues while Judson turns the event into a spectacle.