Stetson Kennedy, a folklorist and social crusader who infiltrated the Ku Klux Klan in the 1940s and wrote a lurid exposé of its activities, “I Rode With the Ku Klux Klan,” died on Saturday in St. Augustine, Fla. He was 94....

Mr. Kennedy developed his sense of racial injustice early. A native of Jacksonville, Fla., he saw the hardships of black Floridians when he knocked on doors collecting payments for his father’s furniture store. His social concerns developed further when he began collecting folklore data for the Federal Writers’ Project in Key West, Tampa and camps for turpentine workers in north Florida, where conditions were close to slavery.

After being rejected by the Army because of a bad back, he threw himself into unmasking the Ku Klux Klan as well as the Columbians, a Georgia neo-Nazi group. He was inspired in part by a tale told by an interview subject whose friend had been the victim of a racial murder in Key West....

William Stetson Kennedy was born on Oct. 5, 1916, in Jacksonville, where he developed an interest in local turns of phrase and sayings that he called “folksays,” jotting them down in notebooks.

While attending the University of Florida, where he took a writing course with Marjorie Kinnan Rawlings, he struck out on his own to do field work in Key West. There he married the first of his seven wives, a Cuban who gave him entree into the local émigré community for his folklore work. While gathering material for the Federal Writers’ Project, he traveled across Florida with the writer Zora Neale Hurston.

His Florida research found its way into “Palmetto Country” (1942), a folkloric survey of territory from southern Alabama and Georgia down to Key West, and the series American Folkways, edited by Erskine Caldwell. In 1994 he returned to folklore in “South Florida Folklife,” written with Peggy Bulger and Tina Bucuvalas, and “Grits and Grunts: Folkloric Key West” (2008)....