The core of the Samuel L. Mitchill papers consists of fourteen letters from Samuel L. Mitchill to his wife Catherine, written from Washington in 1807. These letters describe in vivid detail not only matters of domestic government and international policy, but Washington society as well. Mitchill served in the Senate during a particularly interesting period, and comments at length on Aaron Burr's trial for treason, the political parties, American relations with European nations, and western exploration coming in the wake of the Louisiana Purchase. Mitchill's eclectic interests are reflected throughout these letters. These letters also provide a glimpse into Mitchill's relationship with his wife, apparently a deeply caring, even tender one. In addition to the 1807 letters, there is one letter each written in 1802 and 1812.
The Mitchill papers contain four letters of Catherine Mitchill, all written from Washington to her sister Margaret Miller in New York, 1806-1812. Catherine's letters are as literate and eclectic as her husband's, and are full of gossip from the District of Columbia, providing an excellent view of the capital as seen by the wife of a legislator. Among Catherine's more amusing letters is the one in which she describes a young congressman who entered the wrong hotel room on his wedding night (letter 27). Five of Margaret Miller's letters to Catherine, written from New York, 1808-1812, rival her sister's letters for quality. Miller's letters resemble Catherine Mitchill's in their concern for elite social life, though in New York City, rather than Washington, but they are also a very useful source for the study of marital relations of the period. At the time, Miller's husband, Sylvanus, was serving in the state legislature at Albany, with Margaret left alone to carry on the family's business affairs in her husband's absence, and doing very well at it. Her letter (number 20) in which she tries to persuade her husband to give up politics and come home to the family is of particular interest.