The records of the American Colonization Society span the years 1792-1964, with the bulk of the material concentrated in the period 1823-1912. The records include a variety of material, but in terms of content and physical size the various correspondence series predominate. The society's major interests and activities changed in emphasis during its long history, and this change is reflected in the voluminous correspondence, which ranges in subject from routine administrative and financial matters to the problems of slavery, the status of slaves and freedmen in society, and the advantages and disadvantages of emigration and colonization. The collection is organized in seven series: Incoming Correspondence, Outgoing Correspondence, General Correspondence, Financial Papers, Business Papers, Subject File, and Miscellany.

During the decades prior to the Civil War, the society sought to implement its solution to the slavery problem – colonization of Negroes in Africa – by establishing the colony of Liberia on the west coast of Africa and raising money to transport and support emigrants. Also during this period the society came under attack from critics, particularly William Lloyd Garrison and other abolitionists, who termed it proslavery and succeeded in winning over some previously ardent colonizationists, notably Gerrit Smith, a major contributor to the society's efforts prior to 1835. The efforts of the society to maintain neutrality on the slavery issue and to appeal to all sections of the country are also reflected in the correspondence. Notable correspondents of the pre-Civil War period include Lyman Hotchkiss Atwater, Benjamin Coates, Elliott Cresson, John H. Eaton, Henry Leavitt Ellsworth, Reverend R. S. Finley, Thomas R. Hazzard, Silas Howe, John H. B. Latrobe, John Maclean, and Anson Greene Phelps. An index to incoming correspondence for the period 1839-1855 is located in at the end of the Domestic Letters subseries of the Incoming Correspondence series.

Correspondence in the collection also reveals the difficulty the society experienced in obtaining funds to carry on its work. Letters document the largely unsuccessful efforts to get financial aid from the United States Congress and state legislatures, and reports received from agents around the country attest to the difficulty in obtaining individual contributions and the lack of cooperation from various state auxiliaries.

After the Civil War, the society's activities centered primarily on helping people who wished to emigrate and on providing funds for their support after arrival in Liberia. The correspondence, accordingly, is concerned mainly with obtaining funds for these purposes through private contributions and with counseling those who wished to emigrate. Letters requesting help in moving to Liberia are numerous until 1910, when the activity of the society in this area diminished. Lists of applicants for passage to Liberia appear in the correspondence during the late-nineteenth century as well as in separate registers and rolls contained in the Subject File series. Major figures in the society in this later period were William Coppinger and William McLain. Correspondents include D. C. Haynes, John H. B. Latrobe, John Orcutt, and Joseph Tracy. A large number of communications are from the firm of Yates & Porterfield of New York, through which the society arranged passage to Liberia for the emigrants.

After the turn of the century the society was primarily concerned with the support of education in Liberia, and correspondence is devoted chiefly to administrative and financial matters, particularly cooperation with the Phelps-Stokes Fund in support of the Booker Washington Agricultural and Industrial Institute founded at Kakata, Liberia, in 1929.

Throughout its history, the society received reports from Liberia telling of the conditions of the various settlements. Some of the earliest letters were written by Jehudi Ashmun, one of the society's first agents in Liberia, describing the progress and problems of the colony in 1823 and the need for American support. Later reports and dispatches from the colony come from Stephen Benson, Thomas Buchanan, first governor of Liberia under the commonwealth system, Edward W. Blyden, J. W. Lugenbeel, and Joseph Jenkins Roberts (1809-1876), who became the first president of the Republic of Liberia in 1847. There is also correspondence from ordinary settlers in which they relate their travel experiences, describe the settlements they established or into which they moved, and discuss future plans.

Additional records documenting the administrative functions of the society include financial ledgers, account books, and registers of names of contributors and subscribers to the , the society's journal. The original books of minutes and proceedings of the meetings of the society are also in the records as are drafts and manuscript copies of many of the annual reports. Letters from society members and reports from Liberia were often reprinted in the and annual reports. Many letters for the period prior to 1823 survive only in this form. A few letters printed in the annual reports of 1819-1821 were preserved by Peter Force, then printer for the society; these now form part of the Peter Force Papers in the Manuscript Division.