The Phoebe Plant collection (53 items) is mostly made up of personal correspondence between Plant and her friend Martha Barnes, as well as letters to Plant's mother, Rebecca Hearsey. Martha Barnes wrote to Phebe Plant from 1814-1819, often discussing her religious convictions and, on one occasion, a religious experience with an auditory component (April 21, 1818; in letter dated April 16, 1818). In a letter dated March 1815, she discussed her reaction to a book about Harriet Newell. Plant's letters to Barnes are mainly contained in an 18-page set of retained copies, which includes entries dated from December 19, 1814-November 30, 1815. Plant wrote about her Christian convictions. Other items by Plant include a religious diary with infrequent entries (July 2, 1816-June 15, , 12 pages) and a poem "composed on the death of a wife" (1818).
After Plant's death in 1819, Martha Barnes occasionally wrote to Plant's mother, Rebecca Hearsey, offering condolences and reflecting on her friendship with Plant. The collection also contains letters that Rebecca Hearsey received from members of the Judd family and others; an account about the estate of Joseph Plant of Southington, Connecticut; and an invoice addressed to the Hearsey family (June 12, 1815).