The John Greenleaf Whittier Papers are made up primarily of letters sent and received by Whittier. The collection also includes poetry and prose by Whittier, financial records, printed material, and Whittier family genealogical notes. In addition, there are papers concerning the poet's sister, Elizabeth Whittier, and Whittier's cousins, Caroline Johnson (1821-1917), Abby Johnson Woodman (1828-1921), and her daughter Phebe Woodman (1869-1953) who resided with Whittier at Oak Knoll. The bulk of the papers are from the Oak Knoll Collection acquired from Phebe Woodman, and therefore focus on the period when Whittier lived in Danvers, 1876-1890. The collection has been divided into four series.

Series I. Whittier Correspondence: Letters Sent contains over 500 letters dating from 1833 to 1882. The series is arranged chronologically. The series includes letters sent to relatives, to long-time correspondents who shared Whittier's political and literary interests, and responses to some of the vast number of letters he received from admirers. The collection contains an extensive number of letters to his cousin, Abby Johnson Woodman, and her daughter, Phebe Woodman. These letters form a portrait of the poet's daily life chronicling his many illnesses, activities, and visits with his wide-ranging set of friends and acquaintances. There are also many letters to the author Mary Abigail Dodge, who wrote under the name Gail Hamilton. Two letters of particular interest concerning Whittier's early career as a political activities are to H. I. Bowditch (July 8, 1845) regarding Whittier's early career as a political writer, and to Henry Wilson (February 3, 1861) describing Whittier's impulse to let the southern states secede at the start of the Civil War. A note to an unknown admirer (April 29, 1881) discusses the source for several of the characters in the poem "Snowbound." A letter to the Haverhill Gazette, in response to the celebration of his 80th birthday all over the country, claims that he cares more for the goodwill of his fellow man than for his reputation as a poet (December, 17, 1887).

Series II. Whittier Correspondence: Letters Received contains over 1,000 letters dating from 1829 to 1892. The series is also arranged chronologically and indexed alphabetically by name of correspondent. Included in this series are large quantities of letters from friends, colleagues in political and reform activities, relatives, as well as a portion of the vast amount of mail Whittier received from admirers. Letters from James Fields discuss the publication of Whittier's work. Letters from Abby and Phebe Woodman, Lizzie Whittier, and Whittier relatives Ada and Gustavus Cambett concern daily life of some of the people Whittier was closest to. Whittier had a large set of correspondents in literary circles, and the collection contains letters from James Russell Lowell, William Dean Howells, and Oliver Wendell Holmes. A large part of Whittier's audience was composed of women, and he was known for the help and advice he gave to women writers. Letters from Mary Abigail Dodge (Gail Hamilton), Lucy Larcom, Sarah Orne Jewett, Annie Fields, Celia Thaxter, and Elizabeth Stuart Phelps discuss a variety of literary and personal matters. Letters from abolitionist Henry I. Bowditch, Massachusetts Senator Charles Sumner, and Harriet Beecher Stowe reflect Whittier's activity in the anti-slavery movement. The letters of Whittier's distant relative Hannah Neall concern the continuing moral dilemma that the Quaker community felt over the Civil War. Whittier helped the former slave Charlotte Forten, and two letters written in 1863 discuss her career in the North.

Letters from strangers comprised the majority of mail that Whittier received as he grew older. Perhaps the best indication of his inundation is the fact that many of Whittier's poetry manuscripts are written on the backs of 'fan-mail' letters and autograph requests. Letters from Mumford, Underwood, and Duprez all discuss Southerners whose views have been swayed by Whittier's writings. Of the more typical letters, Rockwell's (February 28, 1873) discusses his appreciation of Whittier's writing. See Appendix I for an index to Whittier's correspondence.

Series III. Writings by Whittier include poetry, prose, and printed material. The poetry and prose manuscripts are arranged alphabetically by title (see Appendix II). In addition to the titled manuscripts, there are over thirty unidentified stanzas many of which were written when Whittier was young and were never published. In addition are lists of poems for books, handwritten translations of foreign verse and a copy of the contract for "Snowbound." Of interest in the prose manuscripts is an introduction to "Ichabod", Whittier's attack on Daniel Webster for his defense of the Fugitive Slave Law. The printed material consists primarily of newspaper clippings and reprints of poetry, prose, and memorabilia.

Series IV. Whittier and Johnson Family Papers contains a wide variety of material relating to Whittier's relatives and Oak Knoll. Included here are letters by Joseph Whittier, the poet's grandfather, John Whittier (1762-1830), his father, and Elizabeth Whittier (1815-1864), his sister. Whittier genealogy contains research notes done by Whittier's descendants. Material relating to the Johnson family includes letters, papers, and memorabilia of Whittier's cousins Abby Johnson Woodman (1828-1921), Caroline Johnson (1826-1922), and Phebe Woodman (1869-1953). Included here are the estate papers of Edmund Johnson, father of Abby and Caroline. The series also contains the correspondence of Robert Rantoul regarding his research for his book Some Personal Reminiscences of the Poet Whittier.

This series also includes envelopes of the correspondence sent and received by Whittier as well as photostats of Whittier letters in other repositories which were collected by the Essex Institute in the 1940s and 1950s.