The correspondence (1869-1883) is primarily routine business, i.e. navy orders and letters of recommendation, and also includes some personal letters. In addition, there are several notebooks and diaries, including notes from Pennsylvania Hospital clinical lectures, 1867-1869 (2 v.); diaries, 1865-1875 (7 v.); a volume of poetry; and general study notes. There is also early material (1745-1813) on the Cassin family, including a letter of indenture dated 1758.

This collection includes letters, diaries, notebooks, and early photographs, relating primarily to the Wister family of Germantown and Philadelphia. Much of the correspondence concerns domestic news and consists of letters from or to Sarah Wister. These include interesting observations on Germantown and Philadelphia society from other families as well, such as the Bayntons and Bullocks. There are numerous letters from various Wisters, including Casper, Charles Jones, Elizabeth (including a journal of a trip to Bristol, 1783), Hannah, John, Owen Jones, and others. There is also poetry by Sarah.

The manuscripts of father William Mitchell and daughter Maria Mitchell are not easily separated, and are treated here together. The collection includes William Mitchell's autobiography, his memoir of Judge Walter Folger of Nantucket, astronomical and meteorological observations, lectures, family and other correspondence.