I can speak to Thomas Jefferson of Monticello and his collection of books.

His father, Peter, was an outdoors kind of guy and never recieved a formal education. He worked as a surveyor and mapped the NC/VA border, Fairfax Line, and drafted the Fry-Jefferson map, but he wasn't much of a reader. Still, he had 40 volumes and upon his death they, along with the bookcase that stored them, went specifically to Thomas, the older brother. This was almost certainly because he had continuously sat reading them as a boy, and referred back to them often. They included a Bible and Prayer Book, works on English history, some volumes from Joseph Addison, an astronomy work, a few books on geography, and several maps. Soon he would be studying under the Rev Maury in Albemarle, learning Latin and Greek, and reading ancient works in their original form.

In the 60s he found himself in Williamsburg, studying law at William and Mary. It was at this time he frequently visited the print shop in which the Virginia Gazette was printed, and for the purpose of purchasing books. He read, and did so often, commonly devoting multiple hours to the task every day. At this time he began to keep a Literary Bible, a record of passages, thoughts, and concepts he wanted to highlight from his reading. It's impossible to say for certain, but it is likely this was the last time Jefferson was able to read fully every thing he purchased.

After returning to Albemarle in the late 60s, disaster struck when his home at Shadwell burned;

We hear from Albemarle that about a fortnight ago the house of Thomas Jefferson, Esq., in that county, was burnt to the ground, together with all his furniture, books, papers, &c., by which the Gentleman suffers a great loss. He was away from home when the Accident occured. Virginia Gazette, Feb 22 1770

Upon learning of the news he immediately asked if any of his books had been saved. "No, Master, all lost" was the response, but with the addition, "but we save your fiddle." In truth some of his books had been at his new project, Monticello, and were safe, but the majority - including his irreplaceable hand drafted legal records of the colony as well as his own legal briefs for his cases - had been lost entirely. For Jefferson it was the first of several major tragedies that would befall him over the next 15 years. As historians, this vital loss of early Jefferson notes and letters is tragic to seeing early Jefferson in great detail. To Jefferson, this served as a reason to duplicate letters, which is partly why we as historians have hundreds of thousands of Jefferson's documents to analyze from his later life.

He immediately began rebuilding the collection and borrowed 100$ from his brother in law and good friend Dabney Carr for the purpose, but soon that was exhausted and more was spent. Within 3 years his collection surpassed that of his Shadwell library.

By the Revolution his library was substantial and ever growing. Upon the death of the great statesman Peyton Randolph, former speaker of the Virginia House of Burgesses and Crowns attorney for the colony, Jefferson purchased his books and legal manuscripts. He did the same of Richard Bland, the great legal scholar. And when the Rev Samual Henley left William and Mary, he purchased his. By the end of the Revolution he inventoried his library. In spring of 1783, by his own count, he had 2,640 different volumes of work.

Soon he was in France and began subscribing to publications there, even subscribing for his friends back home. He sent Madison some 200 volumes alone which covered philosophy, politics, and all manner of topics. But Madison had requested they all be new or relevant, and Jefferson did not disappoint. Madison would use these volumes to study the past and the theoretical before embarking on the biggest project of his early political career: drafting the US Constititon.

The next two decades proved a little busy for Jefferson, yet his collection of books continued to grow at about the same pace. In the War of 1812, a national disaster occured: the Library of Congress was burned by the British. So in the winter of 1814/15, he sold his library to the United States, 6,487 volumes for 23,950$ - it was over twice the size of the lost congressional library. Despite being tens of thousands of dollars in debt to merchants in Bristol (including some of the Wayles debt he inheritted in 1774), he spent the money on more books.

By the end of the 1810s he was working on a new library, one for the school he had just fathered, the University of Virginia. He made recommendations on textbooks to use in the classes in addition to his efforts with the Library itself. He collected books right to the very end of his life, but now he was finally back at Monticello. By his own admission he was riding from an early breakfast to a late supper, leaving very little time to read. In his 80s he nearly drowned in a stream when he fell from his horse, but despite the pleas of family he continued to ride well after he had to be lowered onto the horse from above due to his age and tired old bones. He had taken to writing on rainy days so as to have maximum time to breathe in everything that was Monticello, from the shops on Mulberry Row to the woods of the deer park. He had read in these woods earlier in life with Dabney, and now Dabney, Martha, four of his children and his mother were buried there. Reading just didn't fit into his busy schedule with a couple dozen relatives in the house and 5000 acres to manage, though one visitor did comment that during a discussion he was capable of walking directly to a book, opening it to a passage, reading a relevant bit from it, and then continuing on in the discussion while showing to be highly informed on the topic, no matter what it was. It is not unlikely he had a massive wealth of knowledge about his books and in detail, though it is just very highly unlikely he could have read them all. It was not to show off. He truly could not live without books, from a small boy until an old man.

After his death in 1826 his books were reserved from the first auction, but were then sent to larger cities were they were sold to account his outrageous debt. For the third time, his prized and ever precious collection of works was gone. But thanks to his generosity, the knowledge within was passed on and still lives today as the originating nucleus of the US Library of Congress.

As for what he had, the listing of the nearly 6,500 works named the Catalogue of the library of Thomas Jefferson can be viewed here

My source for this post is almost exclusively the multiple volumes of Dumas Malone on Jefferson titled Jefferson and his Time, (1983), with focus on volumes one, two, and six.

I should add that much, much more could be said about Jefferson alone, and the story of Dr Franklin and his library as well as how he helped start what we think of as libraries is equally stunning, as is the library of William Penn and his sercretary, the very well learned James Logan, who worked with Franklin to start the Library Company of Philadelphia.