In a work of historical fiction, the story takes place in the past, but characters, actions and other details are fictionalized. Creative nonfiction, on the other hand, is a broad term that encompasses many different types of writing (and, it seems worth noting, not all of it is historical). Creative nonfiction that covers the past uses the tools of dramatization but does not fictionalize.
Andrea Barrett's novella “Ship Fever" takes place in 1847 and tells the story of a Canadian doctor serving at Grosse Ile, a quarantine station for Irish immigrants who have fallen ill while fleeing the famine. The novella is based on a very real epidemic. Thousands of people died from typhus on the ships leaving Ireland and thousands more while in quarantine. In 1847 Grosse Ile, on the St. Lawrence River, saw over 100,000 immigrants. The quarantine station was overwhelmed and ships had to anchor in the river and wait for inspectors and doctors. The novella includes a scene that dramatizes this: Dr. Grant, having just arrived at Grosse Ile, boards the ships and sees the devastating conditions. Dr. Grant is a fictional character and the ships he boards are a composite of the details about such ships that Barrett acquired through research. The epidemic as it plays out in “Ship Fever" is anchored in factual detail, and this is the world with which the invented characters--Dr. Grant and others—interact in order to create a shaped plot.
Creative nonfiction that includes historical eras or events does not fictionalize. While it might read like a novel, its task is to remain factually accurate. In A Long Way Gone: Memoirs of a Boy Soldier, Ishmael Beah tells of his experience as a child during wartime in Sierra Leone. It unfolds with the kind of detail and tension you would expect in a novel. When rebels attack Beah's home, he is in another town:
For more than three hours, we stayed at the wharf, anxiously waiting and expecting either to see our families or to talk to someone who had seen them. But there was no news of them, and after a while we didn't know any of the people who came across the river. The day seemed oddly normal. The sun peacefully sailed through the white clouds, birds sang from treetops, the trees danced to the quiet wind . . .
“What are you going to do?" Gibrilla asked us. We were all quiet for a while, and then Talloi broke the silence. “We must go back and see if we can find our families before it is too late."
Here, Beah recounts his own experience. Authors writing about events or eras they didn't experience can also dramatize.
Both historical fiction and creative nonfiction that covers historical events or eras serve to illuminate real events from the past in a compelling and dramatic way. But each has a different relationship with factual accuracy.