The Samuel L. Southard Papers consist of writings, correspondence, printed documents, and other materials. The writings include notebooks, scraps of personal notes, speeches read in public, and drafts of speeches, all in Southard's hand. The notebooks contain primarily legal notes pertaining to Southard's career as a prominent New Jersey lawyer and judge. The books and scraps also contain notes on political and personal matters.

The correspondence documents not only Southard's personal and professional life, but American politics in the first half of the nineteenth century. It includes letters to and from Southard and drafts of letters. Correspondents include many prominent politicians of the time—John Quincy Adams, John Calhoun, Henry Clay, James Madison, and James Monroe all communicated with Southard.

In addition to correspondence, the collection includes a wide variety of documents. There is an extensive record of Southard's legal career including Southard's case notes from many cases. Also included is a significant amount of material on Southard's Congressional career. While not the bulk of the papers, Southard's interest in American Indian affairs and African-American slavery is well-documented and includes some of the most significant material in the collection. There are also several boxes of New Jerseyana containing documents on New Jersey government and business. A significant amount of printed material is also contained within the collection. This includes a number of rare almanacs, journals, pamphlets, speeches—which have been individually cataloged—and several boxes of newspaper clippings.

The Samuel L. Southard papers also contain material pertaining to Southard's father, brother, wife, children, and other personal and professional associates. The bulk of these papers is correspondence, but also included are schooling and financial records. Much of it seems to have been maintained by Southard's son Henry, as many of the documents relate directly to him.