There are a wide variety of libraries available for research in the Washington, D.C. metropolitan area. In addition, the Internet makes other libraries as far away as England and Australia available. Listed here are the most important ones, through which you can start your research and jump to other resources, online or otherwise.
The Edward Bennett Williams Law Library web page and catalog are the first stops in research. The Library's web pages will allow you to access a number of online subscription databases, such as FirstSearch (worldwide catalog of materials in libraries), America: History & Life(primary index for research in American history), Archive Finder, HarpWeek (full text of Harper's Weekly from the Civil War era and early years of Reconstruction), Historical Abstracts, Historical Newspapers Online, Legal Periodicals & Books and JSTOR (full-text backfile of scholarly journals in the fields of history, philosophy, political science and others), and many others. See the list of databases at the beginning of this Research Guide.
The Lauinger Library at the Main campus at Georgetown University is open to Georgetown University Law Center students, staff and faculty. You can check out materials from the library, and go to the library much as you access the Edward Bennett Williams Law Library, but there are separate circulation and access policies governing Lauinger Library. Ask for information about checking out books at Access Services in the Law Center Library, or access their Library web page.
The University of Texas at Austin Law Library Rare Books and Special Collections Department has a pretty good Guide to Legal History Resources on the web. Its emphasis is on U.S. legal history, and Texas legal history in particular. It has become a little outdated, but still very useful.