This novel takes place during the yellow fever epidemic of 1793 in Philadelphia, an actual historical event. The epidemic literally decimated the population of the city, killing 10% of its people. At that time, as the book mentions, Philadelphia was the capital of the country, not Washington, D.C. The doctor mentioned in the novel, Benjamin Rush, was an actual physician who sought to cure the disease through bleeding. Dr. Kerr uses this method in the book to try to cure Mattie's mother of the disease, as Dr. Rush influenced the treatment used by other doctors. Dr. Rush also contracted the disease but survived. 

In the novel, Dr. Rush summons Reverend Allen of the Free African Society to help victims of the disease. This also really happened, as Dr. Rush thought people of African descent couldn't contract the disease, and the African American community thought nursing the sick and burying the dead would help African American people prove their equality to whites. There was a community of freed African American people in Philadelphia at the time, and the character Eliza, who works at the coffeehouse that Mattie's family runs, is part of this community. 

Laurie Halse Anderson sets the narrative firmly in Philadelphia in 1793 by alluding to famous characters who lived during those times and events which took place.  Less than twenty years after the War of Independence, Philadelphia is still the center of government for the United States, and the Cook family's coffee house is located near both the State House where Congress meets, and the newly built residence of President Washington himself.  The author also makes passing references to other political personages, such as Thomas Jefferson and Alexander Hamilton.

Historically, there really was a yellow fever epidemic in Philadelphia in 1793, which changed the face of its population.  Dr. Benjamin Rush was a real person whose philosophies influenced the way in which many patients were treated, and Dr. Jean Deveze was also real, having been the head physician at a hospital for fever victims established at the luxurious Bush Hill residence of Alexander Hamilton himself.

Other historical events incorporated by Anderson to give her book authenticity include Blanchard's hot air balloon launch and the work of the African Free Society.  Jean Pierre Blanchard made the first balloon ascent in America in January of 1793, and Mattie speaks of witnessing the event with Nathaniel Benson (Chapter 5), and Dr. Rush, mistakenly believing that African Americans were immune to the fever, solicited the help of the African Free Society in caring for the city's victims.