What was probably his best-known work came out of the 1940s, when he set for himself the goal of exposing the Ku Klux Klan and its efforts to terrorize blacks throughout the region.
In “The Klan Unmasked,” published in 1954, Mr. Kennedy recounted what he said was his infiltration of the Klan, a secretive organization about whose inner operations little was known.
He wrote that he presented himself as “John S. Perkins,” using the surname of a deceased uncle who was a former Klansman.
Full of dramatic dialogue, the volume reads like a hard-boiled detective novel. Mr. Kennedy’s portrayal of the Klan suggested horrors as well as absurdities.
In the first chapter, Mr. Kennedy tells of receiving a 2 a.m. phone call and finding the chief of the Klavalier Klub murder squad on the line. Before delivering a “fiery summons,” Mr. Kennedy wrote, the chieftain, using a code name, initiated the exchange of passwords.
“White,” his caller prompted.
“Man,” Mr. Kennedy returned.
“Native,” the caller said.
“Born,” Mr. Kennedy said he responded.
In recent years, Mr. Kennedy has been accused of embellishing his account. In a notable episode, Mr. Kennedy’s work was featured in the best-selling book “Freakonomics” by Stephen J. Dubner and Steven D. Levitt.
But in a 2006 New York Times Magazine article, they said they had come to have their doubts about Mr. Kennedy and his work, suggesting that he had worked with an informant and that some of his material came from public events that he attended as a reporter.
Among those coming to his defense were Peggy Bulger, director of the American Folklife Center at the Library of Congress and a personal friend, who vouched for his truthfulness. Acclaimed oral historian Studs Terkel also defended him vigorously.
Mr. Kennedy told the St. Petersburg Times that he did “dramatize” some of his work to help it reach a wider audience.
“It was hardly a cover-up,” he told the Associated Press in 2007.
Mr. Kennedy has been described as providing information about the Klan’s activities to government investigators and the national media. It was part of what he said was an attempt to bring down those he called “homegrown racial terrorists.”
When he was 90, he told the Associated Press that the Klan continued to harass him. He would pick up the telephone to hear threats. “We think about you every time we drive by your house,” the caller would tell him. He cited numerous attempts to burn his home and said that his dog had been shot.
William Stetson Kennedy was born Oct. 5, 1916, in Jacksonville, Fla. On his mother’s side, he was related to hat manufacturer John B. Stetson.
Mr. Kennedy’s awareness of discrimination dated to his teenage years, his wife said, when he was a bill collector for his father’s furniture store.
He began noting the speech of people he met, particularly his father’s African American customers.
Mr. Kennedy dropped out of the University of Florida toward the end of the Depression. He worked as a folklorist with the writers’ project, which was created by President Franklin D. Roosevelt’s New Deal. For his 1942 book “Palmetto Country,” he drove around Florida with a primitive tape recorder, the St. Petersburg Times reported, collecting the stories of orange pickers and turpentine gatherers.
Kept out of World War II military service because of a back injury, Mr. Kennedy worked for the Anti-Defamation League and the Anti-Nazi League of New York. He began his own war on the Klan.
“All my friends were in service, and they were being shot at in a big way. They were fighting racism whether they knew it or not,” Kennedy told the Associated Press in 2007. “At least I could see if I could do something about the racist terrorists in our back yard.”
In 1946, he wrote “Southern Exposure,” a book that documented white supremacists in the South — what a New York Times reviewer called the “funny little native fuehrers, who may not be so funny some day when they are locked up.”
Mr. Kennedy was accused of being a communist and moved to Europe in the 1950s. Existentialist philosopher Jean-Paul Sartre published his book “Jim Crow Guide: The Way It Was” in 1955.
Mr. Kennedy was married seven times. In addition to his wife of five years, of St. Augustine, survivors include a son, Loren Kennedy of Raleigh, N.C.; two stepdaughters, Jennifer Wing Pastore of St. Augustine, Fla., and Nancy Wing Vuehmann of Westminster, Colo.; a stepson, John Howland Wing of Washington; and one grandson.
When he was a boy, Mr. Kennedy was drawn to nature and thought he might be a zoologist.
“I decided to be a zoologist for our own species,” he told the Jacksonville-based Folio Weekly, “to look at the human animal — the most screwed-up and dangerous animal, the only real wild animal on the planet.”