There are only fourteen official Presidential Libraries in America. Why only fourteen when there have been many more Presidents than that? The National Archives and Records Administration was not created until 1934, and The Office of Presidential Libraries did not exist until the Presidential Libraries Act in 1955. This was created in response to the problematic loss of documents and artifacts of past Presidents up until that time.
Presidential libraries and museums from before that period are not a part of the The Presidential Library system, but still play an important role in preserving presidential history, since their holdings might not have survived without these establishments. They may be privately owned or owned by the state, and might not be under obligation to make their items available. Part of the reason why the Presidential Libraries Act was passed was to better organize these kinds of collections and their holdings, and to make accessing materials more uniform.