Paul is the academically precocious thirteen-year-old eldest son of the widowed Oliver Milliron. Plagued by frequent and vivid nightmares, he feels a heavy sense of responsibility for his family and loved ones. His intellect and maturity often make him appear older than his years, causing him to keenly observe the sudden changes occurring in his household and the one-room schoolhouse in Marias Coulee.

Rose is a petite, beautiful, and self-assured young widow from Minnesota who answers an advertisement to become a housekeeper in Montana. She arrives with the firm stipulation that she will not cook, yet she immediately brings order, cleanliness, and a soothing presence to the disheveled Milliron home. She often whistles softly while she works, establishing a tranquil atmosphere for the grieving family.

Introduced as Rose's brother, Morris is a loquacious, handsome young man with a large mustache and an education from the University of Chicago. Although he initially takes on odd manual labor jobs around Marias Coulee, he soon finds himself pressed into service as the new teacher at the one-room schoolhouse. Despite lacking formal teaching experience, he captivates his students with highly engaging educational methods.

Oliver is a physically powerful, articulate homesteader and drayman mourning the recent loss of his wife, Florence. He serves as the president of the local school board and works hard to provide for his three sons through farming and laboring on the Big Ditch irrigation project. As a well-read and sentimental father, he holds high expectations for his children and strives to maintain tranquility in his community.

Damon is Oliver's twelve-year-old middle son, a perceptive sixth grader who equals his older brother in height. Highly interested in sports, he meticulously compiles scrapbooks of football, baseball, and boxing clippings from his father's newspapers. While he enjoys physical roughhousing, he also demonstrates a strategic mind, notably when he intervenes to prevent Paul from engaging in a doomed fistfight.

Toby is the energetic, seven-year-old youngest son of the Milliron family and the only child born in Montana. As a second grader, he is exuberant and full of unfiltered questions. He generally enjoys the affection and protection of his older brothers, the schoolgirls, and even the difficult Aunt Eunice, bringing an innocent joy to the household.

Eddie is the largest and oldest boy in the Marias Coulee one-room schoolhouse, an eighth grader who has been held back twice. He masks his underlying fears and poor eyesight with a thuggish, bullying demeanor, often bruising the younger students. He spends much of his time at school gazing silently around the room, struggling to engage with the material until a new teacher attempts to intervene.

Brose is Eddie's father, a physically imposing and cruel fur trapper whose clothing is perpetually stained from his trade. He carries a large, vicious knife and adheres to strict Pentecostal beliefs, heavily preferring preachers over schoolteachers. His sudden, menacing appearances in the community dictate how others behave, as most citizens fear his explosive temper.

Aunt Eunice is the acerbic mother of George Schricker who resides near the Milliron homestead. She regularly criticizes Paul and Damon, saves all her affection for the youngest, Toby, and constantly predicts her own imminent death. Her woodstove and property require upkeep, which occasionally falls to the Millirons or their hired help.

George is Rae's husband and the son of the difficult Aunt Eunice. He lives near the Milliron homestead and helps provide the grieving family with their one reliable weekly meal. He maintains a quiet presence in the community, often looking worn out by his mother's demanding nature.

Rae is the cousin of Oliver's late wife. She lives with her husband, George, and her difficult mother-in-law, Aunt Eunice. Rae acts as a stabilizing, nurturing presence for the Milliron boys, stepping in to ensure they receive a proper home-cooked meal while their father struggles with domestic duties.

Harry Taggart is an inspector from the Montana Department of Public Instruction. Tasked with evaluating rural one-room schoolhouses, he holds the power to close the Marias Coulee school if it fails to meet state standards. His impending visit causes significant anxiety for the community, though he proves to be an observant and fair evaluator.

Miss Trent is the lone teacher at the Marias Coulee one-room schoolhouse at the start of the 1909 school year. She abruptly abandons her post to elope with a traveling Pentecostal evangelist, leaving the community scrambling to find a replacement to educate their children.

Brother Jubal is a traveling evangelist who sets up a revival tent near the Big Ditch irrigation project. His impassioned religious services attract various community members, including the Turleys, and he eventually causes a local crisis by eloping with the town's only schoolteacher.

Carnelia is a student at the Marias Coulee school and a classmate of Paul's. She participates in the daily routines of the one-room schoolhouse and represents the diverse group of homesteading children who must adapt to a sudden change in classroom leadership.