If there is a particular book you want and you know its title, you can check library catalogs or run a web search or ask a law librarian (who have access to this wonderful resource, Svengalis, “Legal Information Buyer’s Guide and Reference Manual”).
But sometimes you don’t know exactly what you want or even if there are books on the subject you are researching. In addition to checking your local libraries’ catalogs using keyword and subject searches, run a web search using the words free law books. You can also check out these:
1) “Findlaw for the Public,” from the University of Washington Law Library’s Gallagher Blog.
2) Free Nolo Press Books Online. They include Renters Rights, Dog Law, Small Claims Court, and many more are online, FREE, at the Nolo Press website.