Lauren is a 15-year-old Black teenager living in Robledo, a walled community near Los Angeles in 2024. She suffers from hyperempathy syndrome, a condition resulting from her biological mother's drug use that causes her to physically feel the pain and pleasure of others. Secretly convinced that her neighborhood's walls will eventually fail, she studies survival skills, packs emergency bags, and develops a personal philosophy and religion she calls Earthseed. She is practical, forward-thinking, and determined to survive the worsening climate and economic collapse.

Reverend Olamina is a Baptist minister, a college professor, and the primary leader of the Robledo community. He insists that the neighborhood association maintain weapons and perform regular watch shifts to protect against intruders. Rooted in traditional patriarchal structures, he believes in fighting for his home and attempts to shelter his family from the worst realities of the outside world, though his strict disciplinary methods sometimes alienate his children.

Bankole is a 57-year-old doctor who encounters Lauren's group on the highway. Having lost his wife to violence in San Diego, he travels north seeking a safe haven on land he owns. He quickly bonds with Lauren over their shared African surnames and becomes a stabilizing, compassionate presence within the traveling group. Though skeptical of Earthseed's spiritual claims, he supports Lauren's vision.

Keith is Lauren's younger brother. Angry, spiteful, and eager to prove his manhood, he rejects the safety and discipline of Robledo. He steals keys and weapons from his parents to venture into the chaotic outside world, preferring the violent individualism of the streets to his father's community-oriented rules. He is an opportunist who uses his literacy to gain favor with dangerous street gangs.

Cory is Lauren's stepmother and a schoolteacher in the Robledo neighborhood. She misses the technological comforts of the past and often expresses a desire for life to return to normal. She heavily favors her biological son, Keith, often defending his reckless actions and blaming others when his behavior causes trouble for the family.

Harry is a resident of Robledo who travels north with Lauren. Good-natured and traditionally honorable, he struggles to abandon the moral codes of the old world. He is often disturbed by the cold-blooded actions required to survive on the road, viewing Lauren differently once he realizes what she is willing to do to keep them alive.

Zahra is a young woman who escapes the destruction of Robledo and joins Lauren's group. Having experienced homelessness and street violence before her marriage, she possesses vital practical knowledge about surviving outside the walls. She uses the journey north as an opportunity to reinvent herself, asking Lauren to teach her how to read and write.

Joanne is Lauren's best friend in the Robledo neighborhood. When Lauren tries to share her preparations and fears about the community's inevitable collapse, Joanne becomes overwhelmed and reports the conversation to her parents, preferring denial over the frightening reality.

Curtis is a teenager in Robledo and Lauren's early romantic interest. He wants to marry Lauren and live a traditional life within the community, unaware that she views such a path as a death sentence in their deteriorating world.

Richard Moss is a prominent resident of Robledo who has created his own religion blending Old Testament values with West African practices. He operates a patriarchal, polygamist household, employing strict control over his wives and children.

Travis is a traveler heading to Seattle to find work with his family. After Lauren assists them against scavengers, he joins her group. He acts as an intellectual sounding board for Lauren, challenging her ideas about Earthseed and ultimately becoming her first convert on the road.

Natividad is a young mother traveling north with her husband after fleeing an untenable employment situation. She is initially suspicious of strangers but quickly warms to Lauren, showing interest in her poetry and ideas.

Allie is a young woman who joins the Earthseed group alongside her sister after Bankole and Lauren rescue them. Fleeing an abusive father who forced them into sex work, she seeks stability and readily accepts the responsibility of caring for a young orphan in the group.

Jill is Allie's sister, rescued by Lauren and Bankole during an earthquake. She is grateful to the group for saving her life and travels with them, participating in reading lessons and discussions about Earthseed.

Emery is a former debt slave who travels with her young daughter. Escaping extreme corporate exploitation after her husband died and her sons were taken, she cautiously joins Lauren's group in hopes of finding security.

Grayson is a wary, formerly enslaved man trying to keep his daughter alive on the dangerous northern highways. He is highly skeptical of Lauren's communal philosophy but agrees to stay with the group because it offers safety and companionship for his child.

Mrs. Sims is a devoutly religious neighbor of the Olamina family. After experiencing a home robbery and learning that her extended family died in a fire, the isolation and despair overwhelm her, leading her to die by suicide.

Amy is a neglected three-year-old child living in Lauren's neighborhood. The product of familial abuse, she is largely ignored by her family, prompting Lauren to intervene and bring her into the community school.