Just recently, I've acquired a few books that all purport to be "encyclopedias" of Sherlock Holmes. Interestingly enough, two of them have almost the same title: one is Encyclopedia Sherlockiana by Matthew E. Bunson, which has on its cover the subtitle "The Complete A-Z Guide to the World of the Great Detective;" the other is The Encyclopaedia Sherlockiana by Jack Tracy, and its subtitle reads, "A Universal Dictionary of Sherlock Holmes and his Biographer John H. Watson, M.D." The third book I acquired has the much more prosaic title of The Sherlock Holmes Encyclopedia (by Orlando Park). and it is the smallest of the three books: basically, a fairly brief dictionary of Sherlock Holmes characters and locations. A little too brief to be called an "encyclopedia," I think.
Of the three books, the Bunson Encyclopedia Sherlockiana is the most useful volume. The author includes some very useful information about Sherlock Holmes in film and television, Sherlock Holmes societies, a brief bio of Sir Arthur Conan Doyle, and all kinds of other information that was pretty up-to-date as of the book's publication date of 1994. The Tracy book with the same name is a bit more concise in its entries, and the layout is a little crowded and harder to read than Bunson's guide. Tracy does not concern himself with film versions or other non-canonical sources. Park's book, as mentioned above, is by far the briefest of the three guides, and is really more of a glossary than an encyclopedia.
As single volume resources, these books are nice additions to a Sherlockian's library, particularly the book by Bunson. It's a little easier to find useful facts in these books than it is to comb through larger, annotated editions of the Holmes canon, such as Klinger's New Annotated, or Baring-Gould's Annotated. I think there may be a few other Sherlock Holmes "reference books" out there. The Alan Barnes book Sherlock Holmes On Screen has been a handy reference to film and TV adaptations that I've used for many years. I would be interested in hearing about other reference books that I haven't discovered yet, so please feel free to share those with me in the Comments section below!
I'm a stay-at-home dad, and Director of Music Ministries at a United Methodist Church in Mt. Juliet, TN, and a longtime fan of Mr. Sherlock Holmes.