Catherine is an Irish immigrant and dairy worker in her mid-thirties who lives on Chicago's West Side. She runs a small milk business to support her family, operating out of a wooden barn packed with hay and animals. Despite the official inquiry eventually clearing her of wrongdoing, she becomes the immediate target of press rumors claiming her cow kicked over a lantern to start the fire.

Joseph is a 20-year-old reporter for the Chicago Evening Post who documents the disaster from street level. He observes the fire department's early failures and the frantic crowds at chokepoints like the Randolph Street Bridge. His initial bias against working-class neighborhoods reflects the attitudes of Chicago's professional class.

Horace is the editor-in-chief and co-owner of the Chicago Tribune. As a prominent member of Chicago's elite, he places immense confidence in the city's modern infrastructure and allegedly fireproof buildings. His perspective represents the wealthy establishment, and his subsequent reporting emphasizes order and polite behavior over panic.

Claire is a 12-year-old girl whose family recently moved to Chicago. Her experience demonstrates the sheer terror of the evacuation as she becomes separated from her parents in the dense crowds. She relies on her own instincts to seek shelter in a brick-lined alley as the flames surround her.

Alexander is a New York State Assembly member visiting relatives in Chicago. He provides an outsider's view of the disaster, documenting the panic and disorder in the city's wealthier districts. He spends the night frantically searching for his sister-in-law's children through barricaded streets and collapsing bridges.

Julia is a widowed artist caring for five young children and her elderly parents. She demonstrates immense logistical planning and physical effort during the disaster. She negotiates with a landlord to haul her trunks and safely leads her large family to the open prairie.

James is a former Chicago alderman and Civil War veteran with practical knowledge of ordnance. He takes independent initiative when the fire department becomes overwhelmed, securing gunpowder to blast apart houses along Harrison Street. His actions reflect the difficult choices required to halt the fire's advance.

Robert is Chicago's chief fire marshal, tasked with coordinating a small, exhausted force of 185 firefighters against the rapidly expanding blaze. He deals with equipment failures, broken hoses, and severe wind conditions. His men are already fatigued from fighting a major fire the previous night, leaving them poorly equipped for the catastrophe.

Mathias is a 40-year-old watchman responsible for identifying fires and sounding the alarm for the city. He misjudges the location of the O'Leary barn fire due to smoke and distance, sending the first engines nearly a mile away from the actual emergency.

William is the courthouse fire-alarm telegraph operator. When his supervisor realizes a mistake in the initial alarm location, William stubbornly refuses to strike the corrected box, fearing it will cause confusion. He later sends unauthorized alarms once the fire is entirely out of control.

Daniel is a one-legged wagon driver who raises the first alarm about the fire. He rushes into the burning barn to free the trapped animals, losing his wooden peg leg in the floorboards and barely escaping with a calf.

William is a neighbor of the O'Learys who attempts to report the fire early on. He runs to a nearby drugstore to use the alarm box but is turned away by the owner, forcing him to return home and protect his family directly.

Bruno is a drugstore owner whose shop houses a municipal fire-alarm box. He dismisses early warnings about the fire, insisting that an engine has already passed, which prevents an accurate early alarm from being sent to the fire department.

John is a fire department foreman who attempts to turn in a second alarm at Goll's drugstore. In his haste, he pulls the lever only once instead of four times, failing to trigger the necessary reinforcements.