A repository for digital collections. Items in the public domain (works published before 1923) are freely accessible online.

A digital library of Internet sites and other cultural artifacts in digital form. Includes digitized books, periodicals, media, and more.
Legal history and government documents. Contains the entire Congressional Record, Federal Register, Code of Federal Regulations, U.S. Reports, and entire databases of treaties, constitutions, case law, world trials, international trade, foreign relations, and more.
You can find some primary sources in books. Below is a list of relevant subject headings. When searching for these in the catalog, try adding "sources", "documents", "correspondence" to your search.