Prior to the establishment of the Brooklyn Public Library by an Act of Legislature of the State of New York in 1892, Brooklyn was served by a number of independently operated libraries that were open to the public, but which in many cases required a membership fee to use. In 1857, the Mercantile Library Association of the City of Brooklyn was established, and the Mercantile Library of Brooklyn subsequently opened in a building shared by the Brooklyn Athanaeum and Reading Room. In 1865, the Brooklyn Library Association of the Eastern District was established for the purpose of establishing a library in Brooklyn's Eastern District, and in 1868, the Law Library in Brooklyn was established.
In 1888, the Pratt Institute established the first free public library in Brooklyn. This was followed by the opening of several more free public libraries, including the Bay Ridge Free Library and the Long Island Free Library on Atlantic Avenue in Brooklyn. Following the New York State Assembly's approval of the establishment of the Brooklyn Public Library, the Brooklyn Common Council passed a resolution approving its establishment in 1896, and the development of the library system continued throughout the 20th century with the help of a $1.6 million donation from Andrew Carnegie to build 21 branch locations.
From the guide to the Early Brooklyn libraries collection, 1852-1901, (Brooklyn Historical Society)