A fascinating new site from the Davies Project at Princeton University is the Database of American Libraries before 1876 . It covers libraries in the continental United States from the time of the first settlements until 1876 (when the first official national listing was compiled). You can search by type of library (including Ladies Society Library and Temperance Library!) to founding date to collection size. And if you have additional information about any of the entries, there is a comment feature built in. Fascinating stuff! Thanks to librarian.net  for the link.