Associated Press, January 2023: reports researcher Andrew McKenzie-McHarg found "conspiracy theory" used as early as 1863 and "conspiracy theorist" in 1962, before the CIA's 1967 memo, so the CIA did not coin it. That does not settle whether the CIA later spread the term.
The earliest use of the phrase “conspiracy theorist” found by McKenzie-McHarg was in JSTOR, published in 1962.
Associated Press, January 2023: reports researcher Andrew McKenzie-McHarg found "conspiracy theory" used as early as 1863 and "conspiracy theorist" in 1962, before the CIA's 1967 memo, so the CIA did not coin it. That does not settle whether the CIA later spread the term.