Lyddie is a 13-year-old farm girl who assumes heavy household responsibilities after her father leaves the family. Driven by a fierce desire to keep her family's farm and reunite her siblings, she works as a servant at Cutler's Tavern before traveling to Lowell, Massachusetts, to become a factory weaver. She possesses high physical endurance and approaches her loom operation with mechanical precision. Though initially socially isolated by her intense focus on earning money, she gradually opens up to the young women around her and develops a thirst for literacy.

Charlie is Lyddie's 10-year-old brother who labors beside her to maintain their Vermont farm through a harsh winter. When their mother hires them out, Charlie works at a local mill, where he is warmly taken in by the miller's family. He easily adapts to an environment free from food insecurity, distancing himself from the extreme poverty of his early childhood and embracing a formal education.

An experienced, generous weaver at Concord Corporation. Diana is an outspoken labor activist advocating for a ten-hour workday, putting her at odds with factory management. She freely offers her time to mentor new employees and demonstrates remarkable patience with young workers struggling to adapt to the loud, fast-paced machinery.

The floor overseer in the Concord Corporation weaving room. He tracks the efficiency of the workers, granting him bonuses when production speeds up. He abuses his authority by targeting vulnerable young female employees, isolating them after hours and using his influence to silence them.

Rachel is the second oldest of the Worthen children, beginning the story as a frail six-year-old. After experiencing neglect in the care of her aunt and uncle, she arrives in Lowell to live with Lyddie. She eventually takes a job as a doffer in the factory, carrying boxes of bobbins through the dust-filled weaving rooms despite her youth and poor health.

A twenty-year-old mill worker from Maine who rooms with Lyddie at boardinghouse Number Five. Having worked in the factories for nearly a decade, she saves her wages to fund her brother's Harvard education while dreaming of attending Oberlin College herself. Her persistent cough signals the physical toll of prolonged exposure to factory dust.

A young Irish immigrant living in The Acre neighborhood of Lowell. She initially struggles to operate the looms and is terrified of the factory environment, frequently distracted by worries regarding her sick mother. She requires extensive guidance but eventually proves capable of running multiple machines.

The son of a local Quaker farmer near the Worthen property. He dresses plainly according to his faith and helps his family run a station on the Underground Railroad. He frequently checks on the abandoned Worthen farm and attempts to build a relationship with Lyddie through letters and visits to Lowell.

Lyddie's mother, who suffers from severe depression and mental instability following her husband's departure. She vacates the family farm to live with her sister, leasing her older children out as servants so she can collect their wages. She demonstrates an inability to care for her youngest daughters, leading to tragic outcomes.

A Black man escaping slavery who rests at the Worthen farm on his journey toward Canada. He speaks with a preacher's cadence and shares his reflections on the nature of freedom with Lyddie. His story profoundly alters Lyddie's perspective on her own labor and liberty.

The cook at Cutler's Tavern who becomes an early mentor to Lyddie. She admires Lyddie's strong work ethic and tells her stories, such as the fable of the frog churning butter, to encourage resilience. She provides Lyddie with food, boots, and travel money when Lyddie decides to leave for Lowell.

Lyddie's uncle, married to her mother's sister Clarissa. He assumes control of the Worthen family assets, selling the farm without Lyddie's consent. He uses the proceeds to institutionalize Mattie while abandoning Rachel at Lyddie's boardinghouse without regard for Lyddie's employment status.

A neighboring Quaker farmer who acts quietly and generously to support the Worthen children. He purchases their calf for a high price to help them survive and utilizes the abandoned Worthen cabin as a safe house for people escaping slavery. He eventually buys the Worthen land from Judah.

The manager of the boardinghouse where Lyddie resides in Lowell. She ensures the mill girls adhere to company policies, helps Lyddie secure her factory job, and occasionally bends the strict house rules, such as temporarily allowing Rachel to stay despite policies against housing non-employees.

One of Lyddie's roommates at Number Five. She adheres strictly to the moral codes expected of the mill girls, insisting on church attendance and lecturing Betsy about the evils of reading novels. She eventually leaves the factory when the workload becomes too strenuous.

Lyddie's four-year-old sister. She leaves the family farm with her mother and Rachel, moving to her aunt and uncle's home before tragically passing away due to poor living conditions.

A physician in Lowell who is called to attend to Lyddie after she is struck in the head by a flying shuttle on the factory floor.

A local miller who takes Charlie in as an apprentice after the boy leaves Cutler's Tavern. He provides a comfortable, fatherly environment and sends Charlie to school.

The miller's wife who warmly welcomes Charlie into her home. She expresses a desire to have a daughter, prompting Charlie to eventually bring Rachel to live with them.

The demanding owner of Cutler's Tavern where Lyddie first works as a servant. She pays Lyddie's wages directly to Mattie Worthen, extracting intense labor from the girl while offering no personal compensation.

The employment agent for Concord Corporation. He operates the administrative side of the factory and relies heavily on the reports of his overseers when determining disciplinary actions against the young women.

Mattie Worthen's sister and Judah's wife. She is described as "delicate," serving as the justification her husband uses to place Mattie in an asylum and abandon Rachel.