His chief benefaction, however, was a bequest of $400,000 for the foundation and endowment of a public library in New York City, since known as the Astor library, and since 1895 part of the New York public library.
The first course of lectures under the benefaction was delivered in 1820.
In Scotland he gave £2,000,000 in 1901 to establish a trust for providing funds for assisting education at the Scottish universities, a benefaction which led in 1906 to his being elected lord rector of Edinburgh University.
He was put out of all need of money by the singular benefaction of Cotta, the well-known Stuttgart publisher, who was part-proprietor of the Constitutionnel, and made over to Thiers his dividends, or part of them.
Regulations as to grants-in-aid were made by the act, with the stipulation that no sum from them should be devoted to the provision or maintenance of any building, or tutorial or other office, for religious purposes, though private benefaction for such purposes is not prohibited.