His library was one of the finest collections of a private individual. It included some 100,000 carefully selected volumes, largely by French writers and especially poets. He catalogued the library himself, dictating or writing the documents which display his expertise and taste. The library was purchased in 1785 by the Count of Artois, brother of the king, who allowed Argenson to retain it his lifetime. This library formed the basis of the Bibliothèque de l'Arsenal since, as grand master of artillery, he had used the Arsenal to house his library.