Those books were dispersed after Jefferson’s heirs reluctantly decided to sell them at auction in 1829 to pay off Jefferson’s debts; auction catalogs survive, but not a record of who bought the books. The retirement collection is the least known of Jefferson’s libraries and one in which classics were represented in disproportionately greater numbers than politics and the law. He cataloged all 1,600 books according to “the faculties of the human mind,” like memory, reason and imagination, and then classified them further. Many were in French or Italian.

“Currently Monticello and the University of Virginia have the largest concentrations of books from the retirement library,” said Kevin J. Hayes, an English professor at the University of Central Oklahoma and the author of “The Road to Monticello: The Life and Mind of Thomas Jefferson.” “This new find would put Washington University among them. The question I would like to answer is: Do they contain any marginalia? Sometimes Jefferson wrote in his books; his marginalia would enhance both the scholarly and the cultural value of the books immeasurably.”

The answer is yes. Jefferson initialed his books (to affirm his ownership), often corrected typographical errors in the texts and also occasionally wrote marginal notes or comments about the substance. Researchers are combing the newly discovered collection to find such notations.

“These books add a dimension to the study of the life of Jefferson at Monticello,” Ms. Tay said. “They expand our understanding and give us a tangible connection. It helps us understand how Jefferson used his books  whether they were well worn, which means he read them often. Some have annotations, and two architectural volumes include notations of calculations that Jefferson made.”