How many books did Ion Idriess write (that were published)? Beverley Eley, Ion Idriess, lists 49 (Major books published by Ion L. Idriess, pp. 372-373). Wikipedia, Ion Idriess - Bibliography lists 53 (excluding Collections) as does this site in its Idriess Bibliography. Paul Feain and Ellie Aroney, Ion Idriess: An Annotated and Illustrated Bibliography, list 57 in their Chronological Index at the back of the book (pp. ix-x). As an aside, we should note that Eley gets some of the years wrong for (first) publication dates: How Must Australia Fight was 1939, not 1938; Forty Fathoms Deep was 1937, not 1939; Scouting (The Scout!) was 1943, not 1942; The Great Boomerang was 1941, not 1943; and Challenge of the North was 1969, not 1968. We should also note that Feain and Aroney also have some chronological anomalies: Prospecting for Gold was published before Lasseter's Last Ride and should precede Lasseter in 1931 in their list; likewise The Desert Column should come before Men of the Jungle in 1932.

Inherent in the question of how many books, is the question of what constitutes a new book. So a book like Gems from Idriess, (first edition 1949), is not considered by some, including the bibliography on this site, as being a new book, because it contains already published material. Gems contained abridged stories from Idriess with an introduction by Colin Roderick (who presumably also did the selection and abridging) and was for schools (Junior Library of Australian Books). Likewise there is a school's edition of Nemarluk, also with an intro by Roderick. My opinion, for what it's worth, is that both these should be considered as Idriess books in their own right.

But Madman's Island 1927 and Madman's Island 1938, though sharing the same title, are quite different books and are generally so considered.

The Stone of Destiny, 1948, had a few print runs before being revised and enlarged and re-titled as The Diamond, 1969. These are different enough to be considered as two books of Idriess. So also The Silent Service 1944 and The Silent Service 1952. The 1952 edition had new material and new illustrations and is also often considered, e.g., by Feain and Aroney, to be a new book.

The book, How Must Australia Fight or Must Australia Fight, 1939, apart from the different covers and titles, is otherwise the same book. No one knows why the cover/ title anomaly exists or which state came first.

But Horrie the Wog-Dog, 1945 had an American edition, Dog of the Desert, also in 1945. Which edition came first was a puzzle (see, e.g., Feain and Aroney, p.58), solved by Clive English from a letter he received: see Horrie the Wog-Dog - true first edition in FAQ this Forum. The Australian edition was first. Apart from the titles and cover (and different publisher - Bobbs-Merril for the American edition), Dog of the Desert also had a different ending (it excluded the postscript describing Horrie's death) and was revised for an American audience - changing some of the Aussie slang, for example. So two books? I think so.

The Great Trek and Headhunters of the Coral Sea, both 1940, came out in a large, pictorial boards format for their first editions, but prints after that were a smaller size, but basically the same books.

Prospecting for Gold is an interesting case. The first edition was only 157 pages, but sold out in 10 minutes (Eley, p.130). The second edition was expanded and revised - to 204 pages. It included a couple of new chapters. The third edition had extra chapters on batteries, amalgamation, cyaniding and opals. The fourth and subsequent editions added Prospecting for Oil by W G Woolnough. My 5th edition is 293 pages, but my 8th is 288 pages, but same material. The extra material added to each of the first four editions warrants them, to my mind, as being different enough to be their own books - as per Horrie, The Silent Service and Stone of Destiny.

Last books for consideration are compilations of Idriess' writings, but published after his death. So Gouger of the Bulletin, 2008, and Gouger of the Bulletin Part II 2013 were compilations of Idriess' Bulletin articles by Jim Bradly, and Ion Idriess Letters, 2023, collated by Dr David A. Paterson, although containing the writings of Idriess, were not his published works. I would therefore discount posthumous books and include only those published in his lifetime: how many books did Idriess publish in lifetime is probably the question. So how many? I reckon there is a good case for 61!