- Matthew Harrison Brady, a three-time presidential candidate and nationally known attorney. He is a Populist and still a dynamic public speaker, even though he is in his late 60s or early 70s.
- Henry Drummond, another nationally known attorney who was once Brady's closest friend and political confidant. He is about the same age as Brady.
- Bertram "Bert" Cates, a Hillsboro high school teacher in his 20s who has taught the theory of evolution in violation of a state law banning its teaching in classrooms.
- E. K. Hornbeck, a reporter for the fictional Baltimore Herald newspaper. He is young, sarcastic, cynical, and deeply opposed to religious belief.
- Rachel Brown, the Rev. Brown's daughter. She is 22 and the romantic interest of Bertram Cates. Her loyalties are torn between her father and Cates, and she is easily manipulated by others.
- Reverend Jeremiah Brown, a fundamentalist Protestant Christian preacher of unknown denomination who believes in Biblical literalism. He is widowed, and Rachel's father.
- The Judge, a local judge who is subtly sympathetic to Rev. Brown's views.
- Howard Blair, a 13-year-old high school student who was in Bertram Cates' class.
- Melinda Loomis, a 12-year-old girl who believes strongly in the Bible.
- Tom Davenport, the local district attorney who prosecutes Bertram Cates.
- The Mayor, the top elected official of Hillsboro who is openly supportive of the Rev. Brown but also deeply political and concerned about the economic future of his town.
There are also a number of minor speaking roles. These include Meeker, a bailiff at the Hillsboro courthouse; Mrs. Sarah Brady, Matthew Harrison Brady's wife; Mrs. Krebs, a loudly outspoken supporter of Rev. Brown and leader of the Ladies' Aid Society; Mr. Bannister, a local citizen; Elijah, an illiterate man from the nearby woods who sells Bibles to the crowd; Harry Esterbrook, a radio reporter from Chicago; Jesse Dunlap, a local farmer; George Sillers, an employee at the feed store; and the Storekeeper, Sillers' employer.
