In The Baylors of Newmarket (iUniverse, 2009), Thomas Katheder has written a biblio-biography of two generations of a Virginia planter family. It is an excellent survey of the literature and sources on colonial and early national-era private libraries in Virginia, including the types of books typically (and atypically) seen, the relative size of collections, and the methods by which books were obtained.
Katheder focuses on Col. John Baylor (1702-1772) and his son John Baylor IV (1750-1808). The former's letterbooks, probate inventory and purchase records from the Virginia Gazette allow us to reconstruct his library nearly completely (and I have done so here, by working with Mr. Katheder). The colonel's son added significantly to the library, which numbered between twelve and thirteen hundred volumes at the time of his death. Unfortunately no inventory of the library was made at that time, so we are unable to know with certainty what specific books John Baylor IV added to the collection. Katheder takes a good stab at the question, though, suggesting authors and types of books that John Baylor IV probably acquired during a European stay in the late 1770s (a source he thought might have been a list of books in the collection, however, has turned out to be something different, a list of European authors copied directly from Jedidiah Morse's American Universal Geography).
The book itself delves deeply into the transatlantic literary culture of the eighteenth century, and into the precarious financial state of Virginia planters (Baylor would within the span of a few years pay the highest price ever paid in colonial America for a horse - 1,000 guineas for Fearnought in 1764 - and then at his death be deeply in debt, probably insolvent). The curse of the Baylor clan seemed to be that they hadn't much head for business, but they certainly knew and cared about their books. That much is clear from Katheder's fine and detailed study.
The endnotes Katheder provides are superb, and add much to the content and context of the study.