Correspondence (1818-1849, n.d.) consists of letters by and to Lyon that concerning her activities as an educator, particularly her work as founder and principal of Mount Holyoke Female Seminary, and aspects of her personal life. Numerous letters describe the search for a location for the school, efforts to funds, and design, construction, and furnishing of the Seminary Building. Many other letters are by and to women who wished to attend Mount Holyoke or individuals recruiting teachers and missionaries to work in schools in the United States and other countries. There are also letters from Lyon's former pupils, often describing their experiences as teachers. Personal letters in the collection concern Lyon's religious views, her finances, and events affecting members of her family, such as the mental illness of her sister, Lovina Lyon Putnam. Correspondents include her friends and colleagues Zilpah Grant Banister and Eunice C. Cowles; Mount Holyoke trustee William Tyler; Hannah Porter (wife of Trustee Andrew Porter); L.T. Guilford (a Mount Holyoke graduate who established a school for girls in Cleveland, Ohio); Thomas White of Ashfield, Massachusetts (Lyon's friend and financial adviser) and his daughter, Hannah White; Lyon's niece, Abigail Moore Burgess, who served as a teacher at Mount Holyoke and a missionary in India; Laban and Elizabeth Wheaton (founders of Wheaton Female Seminary in Norton, Massachusetts); the Reverend Charles C. Beatty (principal of a school in Steubenville, Ohio); and Justin Perkins (missionary to the Christian Nestorians in Persia).

Writings (circa 1827-1849, n.d.) contains Lyon's published works and her unpublished lists, notes, and other documents. Her publications consist of pamphlets that she wrote between 1834-circa 1840 describing the goals, location, curriculum, requirements, regulations, application process, and domestic work system at Mount Holyoke Female Seminary. The collection also includes her 1843 book, the , which reflects her commitment to supporting the work of foreign missionaries. Some of the unpublished materials date from her studies at Byfield Seminary (1821) and Sanderson Academy (1827-1828). These documents consist of her compositions and lecture notes as well as her hand-drawn map of the United States. Unpublished writings from her years as a teacher and administrator at Ipswich Female Seminary date from about 1830-1834 and include notes for her religious instruction of and talks to students, her lectures on "intellectual philosophy," notes for teachers' meetings, and lists of books, chemicals, and other supplies at the school. Writings relating to Mount Holyoke Female Seminary (circa 1833-1848, n.d.) include plans for the Seminary Building, financial records, lists of applicants, and notes about the domestic work system. The remaining materials in this series consist of documents organized into subject categories (circa 1833-1849, n.d.). These items include a journal the she kept during her travels in Pennsylvania, New York State, and Michigan in 1833, notes reflecting her ideas about education and teaching, her comments on some of her readings, a list of members of her family, and descriptions of her personal property.

Contains notes by Mount Holyoke Female Seminary students and others on Lyon's lectures and talks on religious and secular subjects, circa 1837-1849. Topics of her remarks include religious faith, humility, charity, service to others, behavior,character, fashion and dress, the purpose of education, and teaching methods.

Biographical Material chiefly consists of reminiscences, books, articles, newspaper clippings, and unpublished papers and essays dating from 1849 to the present that concern Lyon's life and work. These materials include the sermon preached at her funeral in 1849 and on the one hundredth anniversary of her birth in 1897, biographies of her by Edward Hitchcock (1851) and Elizabeth Green (1979), recollections by her by Mount Holyoke alumnae (1905-1908) and articles relating to the United States postage stamp issued in her honor in 1987. Other honors conferred upon Lyon are documented by materials relating to her selection to the Western Massachusetts Entrepreneurship Hall of Fame (2005) and to a sculpture of her by Lu Stubbs (2006). An audiocassette in this series is of a radio program concerning (1937). There are also bibliographies of writings by and about Lyon and chronologies listing events during her life. Memorabilia dates from circa 1778 to the present and consists in part of items that Lyon owned, such as her eye glasses, writing desk, and the green velvet bag that she used to collect donations for Mount Holyoke Female Seminary. These materials also include examples of her weaving, scraps of her dresses, and jewelry that incorporates locks of her hair. Other memorabilia consists of jewelry and other objects not directly relating to Lyon. Some of these items were once part of the established at Mount Holyoke in 1904 and dismantled at a later date. Memorabilia also includes the medal from her induction into the National Women's Hall of Fame (1993) and two portraits of Lyon: an ivory miniature from 1832 and a watercolor by Katharine Baldwin Sullivan from 1893.

Mary Lyon's library consists of books that she owned. These volumes reflect her interest in astronomy, botany, geology, history, physiology, and religion and include works by Catharine Esther Beecher, Amos Eaton, Edward Hitchcock, and John Milton. This series also includes a biography of Lyon's teacher and mentor Joseph Emerson.

Lyon Family material consists of manuscripts relating to members of Mary Lyon's family as well as articles and genealogies about the Lyon family in the United States and Europe. Materials concerning Lyon's brother, Aaron Lyon, consist of a list of his children (1839) and a letter that he and one of his sons wrote to another son in 1836 discussing family matters. Genealogical material includes charts showing the ancestries of Lyon's parents and several books and articles about the Lyon/Lyons family. There is also a photograph album (circa 1860s-circa 1900) that appears to contain portraits (including tintypes) of Mary Lyon's brother, Aaron E. Lyon, and his relatives.

Contains pamphlets, newspaper and magazine article, maps, postcards, drawings, photographs, and other material relating to Ashfield, Buckland, and Byfield, Massachusetts. These items include histories of Ashfield and Buckland and an to the Mary Lyon birthplace property in Buckland. Drawings and photographs of that site including an 1883 engraving and copies of a 1905 painting by Edwin Romanzo Elmer. A publication entitled mentions Lyon's father, Aaron Lyon. Postcards and photographs include images of the one-room schoolhouse that she attended in Buckland and the room that she used while loving with the Thomas White family in Ashfield.

Consists of prints of formal photographs and portraits of Lyon dating from her lifetime as well as likenesses created after her death. Includes reproductions of an ivory miniature painting (1832), a daguerreotype (1845) and a ferrotype (circa 1845) of Lyon, and copies of portraits of her by Joseph Chandler (1844) and Louise Rogers Jewett (1906).

Most of Lyon's correspondence and writings in this collection were microfilmed in 1987 as part of a project funded by a grant from the National Historical Publications and Records Commission. There are four sets of the microfilm (four reels per set) in the collection, along with guides and other documents relating to the use of the film. The documents include photocopies of letters by and to Lyon acquired by the Mount Holyoke College Archives and Special Collections after the completion of the microfilming project.

Contains oversized items described as part of other series in the collection. In the container list, descriptions of these items include an indication that they are shelved in Folio.