Every president since Calvin Coolidge has one, and all the ones since Hoover are operated by the National Archives. The half dozen or so remaining libraries are usually operated by states or counties.
It is a practice that should be ditched in favor of more practical solutions. Libraries were needed before the time of the Nook and Kindle, and I still love my paper books, but fewer and fewer people are using hard copy libraries, so it could be time to save the dough and just put everything online.