The cause was complications from multiple sclerosis, said her daughter, Suzanne Karr Schmidt.
In a life that took her from a New Jersey chicken farm to the makeshift ring of Finley's Gym, a landmark of the Washington boxing scene, Ms. Karr resembled the independent-minded boys and girls who populated her two dozen books for young adults.
She began writing on what she later called a "dare" from her husband, crafting a string of gentle adult romances beginning with the 1984 novel "Light of My Heart." Unlike what she called the "bodice rippers" that dominated the market, the books were focused less on sex than on heartfelt connections, paving the way for her transition to an equally wholesome genre: children's historical fiction.
Her writing was drawn partly from childhood memories — poultry made a frequent appearance — as well as her professional life as a film scholar and movie-theater executive ("In the Kaiser's Clutch," a 1995 novel, featured a pair of twins who star in a World War I-era propaganda serial). But she also supplemented her material with information gleaned from trips around the world and through the Library of Congress, where she launched what she described as a "kamikaze attack" on archival documents.
She tackled the skull-measuring pseudoscience of phrenology in her 2000 novel "Skullduggery," chronicled Oregon Trail pioneers in the "Petticoat Party" series, which began with "Go West, Young Women!" (1996), and imagined the inner life of a camel in "Exiled" (2004), a dromedary's first-person account of the Army's 19th-century "Camel Corps."
Her best-known novel, "The Great Turkey Walk" (1998), depicted a 15-year-old boy's effort to herd turkeys from Missouri to a Denver poultry market, a 900-mile journey based on real-life turkey trots that occurred in the 19th century. "The Seventh Knot" (2003), a thriller centered on a secret German society and woodcuts by Albrecht Dürer, won the Agatha Award for best children's or young-adult mystery novel.
Notable deaths in 2017
Ms. Karr sometimes drew her family into her research, turning summer vacations into road trips that traced settlers' routes to the West. But while her books were filled with scholarly detail, they rarely verged on the didactic, balancing history lessons with action-filled story lines that saw young protagonists resist traditional gender roles or — sometimes literally — fight financial hardships.
"Kathleen Karr can cram more grit, character and action into 169 pages than most authors can in a work twice as long," book critic Bella Stander wrote in a Chicago Tribune review of Ms. Karr's novel "The Boxer" (2000). The book described a poor New Yorker who reinvents himself as a lightweight boxing champion known as "the Chopper," and was honored with the Golden Kite Award for the year's best work of fiction by the Society of Children's Book Writers and Illustrators.
Like much of Ms. Karr's work, the novel was set in the 1800s — a time when public life was, she noted, free of "sex, drugs and rock-and-roll," subjects that she studiously avoided in her work.
"I get rather upset with very contemporary [young-adult] literature that focuses on sex and drugs," she told the reference work "Authors & Artists for Young Adults." "I think kids should be allowed to have a childhood."
Kathleen Csere was born in Allentown, Pa., on April 21, 1946, and raised in Dorothy, N.J. Her father, the son of Hungarian immigrants, was an engineer-farmer whom she fictionalized in "Man of the Family" (1999), about an 11-year-old who supports his family after the sudden death of his father.
She graduated from Catholic University in 1968 with a bachelor's degree in English and three years later received a master's degree in English from Providence College. With her husband, Lawrence Karr, she established a state film archive in Rhode Island and moved to Washington in 1971 to join the American Film Institute.
According to her daughter, she soon left to become general manager of the Washington-based Circle movie-theater chain, after learning that despite promises from the AFI her pay did not match that of her husband, a fellow archivist. She later became Circle's advertising and public-relations director before writing full time. She moved to Chicago from the District in 2017 and died in a nursing home there.
Her husband of 39 years died in 2007. Survivors include two children, Daniel Karr of Beijing and Suzanne Karr Schmidt of Chicago; a brother; a sister; and three grandsons.
Ms. Karr nurtured a longtime interest in archaeology, taking her children on digs in national forests, but she took up a more strenuous hobby — boxing — as "a form of stress relief" in the late 1990s, her daughter said.
"It was during a string of rejections from publishers in New York, when she was fed up and wanted to 'hit something,' as she put it," said Karr Schmidt. With a little research, Ms. Karr found that Jim Finley's gym in Northeast Washington accepted women. She began training around the same time she began planning her boxing novel, which she described as her favorite book.
"My ring scenes are gritty, sweaty and right on," she told the journal Teacher Librarian in 2007, "because I've been there myself."
Read more Washington Post obituaries