The Warner Library became a reality because of the generosity of local residents Worcester Reed Warner and his wife, Cornelia Blakemore Warner. In the late 1920s they undertook to have a library built as a gift to the community. Since a house already occupied the site they preferred, at the corner of Broadway and Wildey Street, Mr. and Mrs. Warner persuaded the Village of Tarrytown's Board of Trustees to have the house moved to the western limit of the property. That building later became the Tarrytown Village Hall. Mr. and Mrs. Warner engaged architect Walter Dabney Blair to design the library building and construction began in 1928.
While construction progressed, the library's first Board of Trustees was organized, with several prominent local residents serving as charter members. An application for the library's charter was sent to the New York State Board of Regents, which issued the charter on January 15, 1929. In recognition of the efforts of Mr. and Mrs. Warner, the Library Board determined that the new library should bear their name.
Accordingly, on February 22, 1929, the Warner Library held a dedication ceremony. Many citizens of Tarrytown and North Tarrytown (now Sleepy Hollow) attended the formal ceremony. Mr. Warner died later that same year, while traveling in Germany with his wife. After his death, Mrs. Warner and their daughter, Helen Blakemore Warner, continued their interest in the Warner Library and remained active as benefactors of many community causes.