Events that occurred on 31 July
 On Earth
- 1924 - Actor Garard Green is born.
- 1944 - J.R.R. Tolkien writes Letter 77.
- 1947 - J.R.R. Tolkien writes Letter 109.
- 1960 - J.R.R. Tolkien writes Letter 223.
- 1969 - J.R.R. Tolkien writes Letter 311, concerned with his health.
- 1982 - The third episode of the new version of the 1981 radio series of The Lord of the Rings is aired on BBC Radio 4.
- 1988 - Mythcon XIX in Berkeley, California.
- 1989 - Mythcon XX at University of British Columbia, Vancouver.
- 1993 - Mythcon XXIV at University of Minnesota, Minneapolis.
- 1999 - Mythcon XXX in Milwaukee, Wisconsin.
- 2001 - Author Poul Anderson dies.
- 2004 - The Lord of the Rings Symphony at Heinz Hall in Pittsburgh, Pennsylvania.
- 2004 - Mythcon XXXV at University of Michigan in Ann Arbor.
- 2011 - Picturing Tolkien is published.
 In Arda
- Note: Months of the Shire Calendar only have 30 days, so no events have nor will happen on the 31st.