The Correspondence of Series I includes letters written by Sanders' parents that describe mission work and native customs in Sri Lanka (Ceylon) and give an interesting portrayal of world conditions in the third quarter of the 19th century. While in Sri Lanka (Ceylon) from 1882 to 1886, Sanders received letters from his missionary brothers: Charley in Turkey and Will in Angola. During the period 1926 to 1932 Sanders attempted to trace his family history and received letters from family members supplying applicable information. Correspondence of 1925 includes letters to and from John R. Mott.
The Diaries and Journals in Series II include forty-four personal diaries of Frank Knight Sanders as well as journals describing trips taken by Sanders. The Writings of Series III include lectures, sermons, and articles by Sanders as well as writings of others. Writings by others include extracts from letters written by a Civil War doctor in 1862, anonymous sermons dating from 1815 to 1845, and medical sketches on the subject of "imbeciles" written by Henry Martyn Knight, superintendent of the Connecticut School for Imbeciles. The Printed Material of Series IV includes newspapers clippings, and miscellaneous pamphlets; a few pamphlets related to the Board of Missionary Preparation have been placed in YDSL HR1052. Series V, Personal Items and Memorabilia, contains biographical material, photographs, and genealogical information tracing Sanders' family back to early settlers of America, including Roger Williams of Rhode Island.