Alice is a young Englishwoman who relocates to Baileyville, Kentucky, expecting a glamorous American life. Instead, she finds herself trapped in a rigid, monotonous routine under the watchful eye of her controlling father-in-law. Seeking purpose and an escape from her tense household, she volunteers for the Pack Horse Library. The demanding work of delivering books on horseback challenges her, but it also helps her discover her own resourcefulness and a deep affection for the Appalachian region.

Bennett is Alice's handsome American husband who wooed her enthusiastically in Europe but becomes distant and passive upon returning to Kentucky. He works under his wealthy father and struggles to assert any independence from the older man's dominating influence. Rather than supporting his new wife, he often retreats into the company of his friends and avoids confronting the issues in their household.

Mr. Van Cleve is the wealthy owner of the Hoffman Mining Company and the patriarch of the Van Cleve household. He rules both his family and the town with an iron fist, utilizing his financial power to enforce his traditional worldview. He views the Pack Horse Library as a direct threat to societal morals and actively campaigns to shut it down. His overbearing presence stifles his son Bennett and creates an unbearable living situation for his daughter-in-law.

Margery runs the WPA Pack Horse Library in Baileyville with fierce independence. She carries the stigma of the notorious O'Hare family name, a clan of moonshiners known for violence, but she refuses to apologize for her heritage or conform to the town's conservative expectations. She trusts few people, maintaining an unconventional romance while fiercely protecting her autonomy. As the lead librarian, she braves dangerous terrain and hostile locals to ensure books reach isolated families.

Fred is a quiet, capable local man in his late thirties who breeds and breaks horses. He carries a reputation in Baileyville for being "unmanly" because he refused to beat his unfaithful wife when she left him. Despite local gossip, he becomes a steady supporter of the library project, offering his property, structural help, and quiet encouragement to the librarians.

Beth is a tomboyish librarian who drinks, smokes, and holds her own on a farm full of brothers. She brings a tough, pragmatic energy to the library staff and takes on the physically demanding riding routes to deliver books to rural families. She dreams of traveling the world and chafes against the limitations placed on young women in Kentucky.

Izzy is a young woman who wears a heavy metal-and-leather leg brace due to childhood polio. Initially shy and defensive, she slowly discovers her courage as she learns to ride a gentle horse named Patch. Bonding with the other librarians and the schoolchildren they serve, she finds confidence and reveals a beautiful singing voice.

Mrs. Brady is a formidable, highly respected woman in Baileyville who spearheads the local Pack Horse Library project. She is pragmatic and capable of cutting down opposition, though she also worries about maintaining respectability in a conservative town. She pushes her daughter into service, hoping to draw her out of her shell.

Sophia is a highly organized, intelligent Black woman who returns to Baileyville from Louisville to care for her injured brother. Facing extreme racial prejudice in the divided town, she works behind locked doors to avoid violence. Her exceptional cataloging skills bring essential order to the chaotic Pack Horse Library.

Kathleen is a hardworking mountain woman whose husband suffers from black lung disease caused by the local mines. Initially just a patron of the library, her gratitude for the book deliveries establishes a warm connection between her family and the librarians. She steps up to help the library when the original riders face crises.

Sven is Margery's partner, a large, protective man who works at the Hoffman Mining Company. He cares deeply for Margery and frequently proposes marriage, though he struggles to navigate her fierce need for independence and her refusal to be tied down by societal conventions.

Clem is an aggressive, drunken man from a family that holds a generations-long blood feud with the O'Hares. He resents the library project and threatens the librarians during their delivery routes. His violent actions set off a chain of events that threaten the entire town.

William is Sophia's brother, a Black man who suffers a severe leg injury while working in the hazardous local mines. His injury prompts his sister to return to the heavily segregated town of Baileyville to nurse him.

Verna is the teenage daughter of Clem McCullough. She lives in isolation and fear due to her father's abusive nature. She is highly distrustful of outsiders but ultimately plays a crucial role in the conflict surrounding the library.

Garrett is Kathleen's husband, a local miner suffering from the advanced stages of black lung disease. He is physically depleted by his years working in the toxic environment of the Hoffman Mining Company.

Jim is a grieving widower living in an isolated mountain cabin with his daughters. Initially hostile and suspicious of the library riders, he slowly softens as the books bring joy and education to his children.

Peggy is a local Baileyville woman who previously pursued Bennett's affections before he traveled to Europe and met Alice. She remains a lingering presence in the town's social circles, contributing to Alice's feelings of isolation.