In genius studies, personal libraries (TR:91), abbreviated (PL:#) in existographies, e.g. Thomas Young (PL:1K), are book collections, generally over the Buffett number (100+), on subjects connected to thermodynamics or human thermodynamics, or bigger "geniuses on" type questions in general.

Overview
At the high end of personal library rankings, there are, primarily in France, who purchased 20,000 to 30,000 libraries in bulk.

List
The following is a work-in-progress ranking of personal libraries of noted geniuses:

#
PersonBooksNotes

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1. John Acton
(1834-1902)
60,000 (Ѻ)
2.Charles Ogden
(1889-1957)
50,000 Collection (Ѻ) contains interesting things, such as collection contains five books from Ben Jonson’s own library, Percy Shelley's annotated copy of Petrarch.

Umberto Eco 75Umberto Eco
(1932-2016)
30,000-50,000 [RGM:308|1,500+] Contained 30,000 at last count (Ѻ) as commented on by Nassim Taleb; quote: “I'm afraid that, by now, it might actually be 50,000 books. When my secretary wanted to catalogue them, I asked her not to. My interests change constantly, and so does my library. By the way, if you constantly change your interests, your library will constantly be saying something different about you. Besides, even without a catalogue, I'm forced to remember my books. I have a hallway for literature that's 70 meters long. I walk through it several times a day, and I feel good when I do” (Eco, 2009) (Ѻ); multiple videos (Ѻ)(Ѻ)
3.French salon owners20,000-30,000Based on several historical accounts of 18th and 19th century salon owners, e.g. Baron d'Holbach; many wealthy salon owners bought whole library collections outright.
4.Emilie Chatelet 75Emilie Chatelet
(1706-1749)
25,000+ (?)Built and ran her own research lab at Chateau de Cirey, from 1734-1749, said to have a library comparable to the Paris academy of sciences; scientists such as Samuel Koenig and Johann Bernoulli, not to mention Voltaire (her lover), would stay for weeks or months at a time.

Harold Bloom 75Harold Bloom
(1930-)
25,000 Bloom (with books)In 2002, had amassed some 25,000 books encompassing most of American and British poetry, criticism, and literary history (Ѻ); said to have a phenomenal ability to speed read and memorize what he's read (Ѻ).
5.Henry Buckle 75Henry Buckle
(1821-1862)
21,000 “In his library, when he died, were eleven thousand books—and these he and carefully digested, beside ten thousand more that he had disposed of when done with them.”
— Arthur Brisbane (1913), “Introduction to History of Civilization in England (pg. vi)
6.Georges Cuvier 75 Georges Cuvier
(1769-1832)
20,000 Said to have twenty-thousand volumes in his library and could “recall in detail the contents of all” (Frenay, 2006); he was also “vain, arrogant, and authoritarian”, liked to think of himself as “second only to Aristotle”. [4] Based on his Biblically-nonsensed periodic flood based creation of species theory, this book memory count is a high end over-exaggeration.

Susan Sontag 75Susan Sontag
(1933-2004)
20,000 Had a library of 20,000 volumes, according to Benjamin Moser’s 2019 Susan Sontag: Her Life. (Ѻ)(Ѻ)(Ѻ)
7. William King
(1663-1712)
20,000-7,000 Is exaggeratedly reported, by charlatan physician hack writer Joseph Browne (Ѻ), to have dedicated himself completely to his studies (Ѻ) at Oxford, during the years 1681 (age 18) to 1689 (age 26), and therein read over 22,000 books and manuscripts; this figure found its way into the mind of Thomas Young who stated, so to perspectively gauge his own reading level, over the course of 50 years, that: “it is said that William King the poet read no fewer than seven thousand in the course of his residence of seven years at Oxford.” This reading rate (1000 books/year) to note, would amount to having read 2.74 books per day, on average, over the course of seven years; which seems a stretch if one was actually to process and assimilate what one has read; Thims, by comparison, on a good day, can read, at the high end, three large books in one day. Some deeper books, however, can absorb ones mental digestion time form months or more. Given that King never produced anything of intellectual note, per logic of the Young read-write formula:

“The longer a person has lived the less he gains by reading, and the more likely he is to forget what he has read and learnt of old; and the only remedy that I know of is to write upon every subject that he wishes to understand, even if he burns what he has written.”
Thomas Young (1809), “Letter to Hudson Gurney” [3]

It is doubtful that King read as much as folklore attributes to him.
8.Kim Peek
(1951-2009)
12,000Person behind the 1988 film Rain Main, who was born without a corpus callosum (the bundle of nerves that connects the two hemispheres of the brain), may have had this ability. He would read books, memorized them, and then placed them upside down on the shelf to show that he had finished reading them, a practice he maintained. He can read a book in about an hour, and remember almost everything he had read, and was thus able to memorizing vast amounts of information in subjects ranging from history and literature, geography, and numbers to sports, music, and dates. His reading technique consisted of reading the left page with his left eye and the right page with his right eye and in this way he could read two pages at a time with a rate of about 8-10 seconds per page. It is believed he could recall the content of at least 12,000 books from memory.
9.Charles Bradlaugh 75Charles Bradlaugh
(1833-1891)
7,000“My father's books were very dear to him, and had always. been so, from the time when as a dragoon he was able to carry the whole of his library in his soldier's knapsack, until the day of his death, when his literary possessions had outgrown all ordinary-sized rooms, and had even swelled beyond the capacity of his work-room at Circus Road. They numbered in all rather over 7,000 volumes, about 3,000 Blue Books, besides a very large number of unbound pamphlets. In many respects the library is essentially a poor man's library. There are only a few rare bindings, and comparatively few costly ‘first editions’ ; now and again there is a volume missing from a set, and here and there a title page is wanting.' But, such as they are, he valued them, all and every one.”
— Hypatia Bradlaugh (1891), The Library of the Late Charles Bradlaugh (Ѻ)
10.Jefferson 75Thomas Jefferson
(1743-1826)
6,700 Jefferson, after inheriting books from his father Peter Jefferson, prior to 1770, noted that by age 40 (1783) he had acquired a total of 2,640 volumes; that by age 46 (1789), upon his return to America, had doubled his library (c.5280 books), and that by 1815 (age 72) he had a collection of 6,700 volumes. [7] On 28 Nov 1814, it is recorded that Jefferson sold 6,487 volumes (for $23,950) to the library of congress, to replenish the 3,000-volumes burned by the British. (Ѻ) Legacy Library: 5,611 (to date) (Ѻ)
11.Goethe 75 newJohann Goethe
(
1749-1832)
5,000At the age of about 80, had a 5,000 book personal library.
12.Arthur Iberall 75Arthur Iberall
(1918-2002)
5,000In 2002, he had 5,000 books; 4,000 of which were donated to library, 1,000 of which were kept by his daughter Thia Iberall; Aristotle was his core hero.
13. James Lawler
(1936-)
4,000+ American chemical-nuclear engineer (Ѻ), curator of NexialInstitute.com (Ѻ), which promotes the social entropy theories of Alfredo Infante, told (Ѻ) Thims (Mar 2006) that he has 4,000+ books, some of which are in triplicate.
13.James Madison 75James Madison
(1751-1836)
4,000[3]
14.Robert Hooke 75Robert Hooke
(1635-1703)
3,000 “Hooke’s magnificent library, collected during a lifetime spent in auction rooms and bookshops, contained many bound pamphlets and over 3,000 books.”
— Stephen Inwood (2002), The Man Who Knew Too Much (pg. 4)
14. Ernst Schumacher
(1911-1977)
2,500 German economist and statistician; protégé of John Keynes; read by Erland Lagerroth; library consists of: critiques of economics, technology, agriculture, and development, there are equally considerable collections of titles exploring Western and Eastern philosophies, a variety of religious and political thought, psychology, and mysticism. Seven hundred of the titles are in German and the remainder are in English. (Ѻ)
15.Thomas Browne 75Thomas Browne
(1605-1682)
2,000+ Over 2,000 titles (Ѻ); subjects: Greek literature, Roman literature, Arabic, contemporary science, philosophy, theology, medicine, esoteric, natural history, literature, geography and history. (Ѻ)
1#.Descartes 75Rene Descartes
(1596-1650)
2,000Descartes teaching Christina (1649)When Christina Alexandra, Queen of Sweden, sent a ship to fetch him (1649), to come to Sweden, to tutor her, the ship brought back him and 2,000 books. Both are shown adjacent, Alexandra, also had amassed a enormous collection of books and manuscripts, which is now in the Vatican library.
16.Walter Benjamin 75Walter Benjamin
(1892-1940)
2,000 Roughly 2,000 books. (Ѻ)
1#.Newton 75Isaac Newton
(1643-1727)
1,752Newton's libraryHad a personal library consisted of 1,752 books, of which 369 were scientific works.

Artist's engraving (Morel, 1874), showing a portion of Newton's library in the background, of apocryphal story of Isaac Newton's pet dog knocking over a candle and setting fire to his papers. Newton had on his table a pile of papers upon which were written calculations that had taken him twenty years to make. [1]
17.John Adams 75John Adams
(1735-1826)
1741 (Ѻ)
18.John Dewey 75John Dewey
(1859-1952)
1687 (Ѻ)
19.Libb Thims 75Libb Thims
(c.1975-)
1,500+ SPE 2015 (5 of 5) (screen shot)In 2007, Thims' personal library stood at just past the 1,000 book mark. [2] In 2011, Thims' total personal library collection, including thermodynamics books, was at the 1,250+ mark.Thims' personal library is predominately polymathic (the core of which being Clausius' Mechanical Theory of Heat and chemical thermodynamics generally); the general predominate division is as follows:

Thims’ thermodynamics book collection | 403+
Thims’ mate selection book collection | 140+
Thims religio-mythology and atheism book collection | 123+
Thims’ list of thermodynamics books to buy

Adjacent photo, from the 2014 "25 Smartest People Alive | Existive" (Ѻ) video countdown, depicts some of Thims person library. A 30 Sep 2015 photo (Ѻ) of library, amid residence move, of circa 1,300 books, aka the "hard drive of Hmolpedia", shows the library contained in: 39 banana boxes and 6 egg boxes. Possibly, at 1,500+ level in 2018.
20.Nietzsche 75Friedrich Nietzsche
(1844-1900)
1,100 Nietzsche personal libraryA photo of some of the books in the personal library in the home of Friedrich Nietzsche. (Ѻ)(Ѻ)
21.Thomas Young 75Thomas Young
(1773-1829)
1,000 “Though he wrote with rapidity, he read but slowly, [and] perhaps the whole list of the works that he studied, in the course of 50 years, does not amount to more than a thousand volumes: while it is said that William King the poet read no fewer than seven thousand in the course of his residence of seven years at Oxford.”
— Thomas Young (c.1825), Autobiography
22.Schopenhauer 75Arthur Schopenhauer
(1788-1860)
818+ (Ѻ)
23.Kurt Godel 75Kurt Godel
(1906-1978)
700 (Ѻ)
24.Einstein 75 (older)Albert Einstein
(1879-1955)
600+Einstein readingCrude visual photo of Einstein’s personal library shows about 600-700 books.

“Throughout his life Einstein was a man of the book, to a much higher degree than other scientists. The remarkably diverse collection of volumes in his library grew constantly. If we look only at the German-language books published before 1910 that survived Einstein’s Princeton household, the list includes much of the cannon of the time: Boltzmann, Buchner, Friedrich Hebbel, the works of Heine in two editions, Helmholtz, von Humboldt, the many books of Kant, Gotthold Lessing, Mach, Nietzsche, and Schopenhauer. But what looms largest are the collected works of Johann von Goethe in a thirty-six volume edition and another of twelve volumes, plus two volumes on his Optics, the exchange of letters between Goethe and Schiller, and a separate volume of Faust.”
— Gerald Holton (2008) [5]
25.Kant 75 Immanuel Kant
(1724-1804)
326(Ѻ)(Ѻ)
16.Leonardo da VinciLeonardo da Vinci
(
1452-1519)
200His person library (Ѻ), which he cataloged in some cases, contains about 200 books (Ѻ), depending on period.

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Quotes
The following are related quotes:

“I seek for learning in this book and cannot find it. Though I study all books from end-to-end, I cannot discover the touchstone of wisdom. O, how unfortunate art thou, Faust! The sleepless nights I have spent in fathoming the mysteries of theology! But, no! By heaven, I will no longer delay, I will take upon myself all labor, so that I may penetrate into that which is concealed, and fathom the mysteries of nature!”
Faust (c.1800), Geisselbrecht’s puppet-play [1]

“I have never met with a man more learned—I may add, more universally learned, than the Baron d'Holbach; and I have never seen anyone who cared so little to pass for learned in the eyes of the world. Had it not been for the sincere interest he took in the progress of science, and a longing to impart to others what he thought might be useful to them, the world would always have remained ignorant of his vast erudition. His learning, like his fortune, he gave away, but never crouched to public opinion. The French nation is indebted to d'Holbach for its rapid progress in natural history and chemistry. It was he who, 30 years ago, translated (enriched with valuable notes) the best works published by the Germans on both these sciences, till then, scarcely known, or at least, very much neglected in France. Holbach possessed an extensive library, and the tenacity of his memory was such as to enable him to remember without effort every thing he had once read ”
— Friedrich Melchior (1789), “On Baron d’Holbach”, Aug 10; note that, in the context of this quote, Melchior (Ѻ) was also closely associated with: Jean Rousseau (IQ:175|#243), Denis Diderot (IQ:175|#243), Jean d'Alembert (IQ:185|#73), Marmontel, Morellet, and Helvetius (IQ:175|#215) [6]

See also
Einstein’s personal library
Goethe’s collected works
Library walk problem
Libb Thims (books read)
Thims’ personal library

References
1. (a) Brewster, David. (1833). The Life of Isaac Newton (image). J. & J. Harper.
(b) Author. (1878). “King Alfred and the Cakes”, St. Nicholas magazine, Vol. 5, No. 4, Feb.
2. Pierce, Charles P. (2009). Idiot America: How Stupidity became a Virtue in the Land of the Free (pgs. 284-85). Anchor Books.
3. Robinson, Andrew. (2006). The Last Man Who Knew Everything: Thomas Young, the Anonymous Genius who Proved Newton Wrong and Deciphered the Rosetta Stone, among other Surprising Feats (self-taught, pg. 15; burn, pg. 179; Lagrange, pgs. 182-83). Plume Books.
4. Frenay, Robert. (2006). Pulse: the Coming Age of Systems and Machines Inspired by Living Things (pg. #). Farrar, Straus and Giroux.
5. Galison, Peter, Holton, Gerald J., and Schweber, Silvan S. (2008). Einstein for the 21st Century: His Legacy in Science, Art, and Modern Culture (ch. 1: Who Was Einstein? Why is He Still so Alive?, pgs 3-15; quote: pg. 10). Princeton University Press.
6. d’Holbach, Baron. (1770). The System of Nature: Laws of the Moral and Physical World (notes by Denis Diderot; translator: H.D. Robinson) (attributed, pgs. iv-v; universally learned, pg. v; translated, pg. v). J.P. Mendum, 1889.

External links
Library – Wikipedia.
Legacy libraries – LibraryThing.com.

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