William Faulkner pronounces & explains Yoknapatawpha County AUDIO of famous writer = As I Lay Dying

When did Faulkner give the name Yoknapatawpha County for the FIRST TIME in one of his works?
It was in the novel As I Lay Dying.
Earlier, he had used Jefferson as a setting. Jefferson is cited in some early stories and in the novel Sartoris/Flags in the Dust. But that's Jefferson--the name he used while thinking of Oxford, Mississippi.
Yoknapatawpha County was not mentioned in these early (pre-1930) works.
In the 1930 novel As I Lay Dying, the county was named for the first time.
During an interview, William Faulkner is asked this: "How do you pronounce the name of your mythical county?"
Faulkner replies, "If you break it down into syllables, it's simple: Y-o-k, n-a, p-a, t-a-w, p-h-a. YOK-na-pa-TAW-pha. It's a Chickasaw Indian word, meaning water runs slow through flat land."
Yoknapatawpha County is a fictional county based on Lafayette County, Mississippi--the land that the novelist knew best. Its county seat is Oxford, where the writer had a home.
The word Yoknapatawpha is pronounced "Yok'na pa TAW pha."
It is derived from two Chickasaw words-Yocona and petopha ("split land"--the writer embellishes by saying it means "water runs slow through flat land.").
Faulkner is speaking to a University of Virginia audience.
Yoknapatawpha was the original name for the Yocona River (a real river near Faulkner's home), a tributary of the Tallahatchie which runs through the southern part of Lafayette County. The spelling of "Yoknapatawpha" varied when it was the river's name.
The area was originally Chickasaw land. Whites settled in the area around 1800.