The longest known diary contains over 37 million words.
Although the Guinness World Record people don't have a record for it, the 25-year, 37.5-million word diary of the Reverend Robert W. Shields is likely the wordiest ever. Every day, beginning in 1972 and ending with a stroke he suffered in 1999, Shields spent four hours writing down the minutiae of his life, from going to the bathroom to detailing all his junk mail.

Shields donated the diary to Washington State University on the grounds that no one read it for 50 years. He died in 2007.