The series contains the personal and professional correspondence of Samuel L. Southard. It includes correspondence both to and from Southard. The material relates to all aspects of his life. Personal correspondence includes letters to and from his family. Southard received many letters in Washington, D.C., from his wife in New Jersey updating him on her medical condition or their children's schooling. As Southard's children grew and moved away, he and his children exchanged letters in order to keep each other abreast of changes in personal and professional life. Much of Southard's correspondence with friends, such as John Taliaferro, runs throughout his life. Southard discussed his family and career with some and politics and social issues with others. Professional correspondence ranges from formal letters announcing political appointments to letters from notable associates discussing political issues of the day. Some are brief memos that appear to be little more than a formality and some contain long conversations on key topics.

Particularly well documented are the presidential elections of 1824 and 1840. The political history of New Jersey during Southard's career in politics is extensively documented, and his correspondence contains many letters received regularly from county leaders in all sections of the state. Also reflected in his correspondence is his relationship with Princeton University and his interest in his Quaker constituents.

Southard's correspondence includes letters to and from many notable politicians and persons of the time including John Quincy Adams, John C. Calhoun, Henry Clay, James Fenimore Cooper, Alexis De Tocqueville, Millard Fillmore, Andrew Jackson, James Madison, James Monroe, Richard Rush, John Tyler, Martin Van Buren, Emma Willard, and William Wirt. Southard also communicated with such prominent New Jerseyans as Mahlon Dickerson, Charles Ewing, Samuel Miller, Aaron Ogden, William Pennington, and Richard Stockton, son of the signer of the Declaration of Independence.