The William H. Channing collection is comprised of 34 letters. Many of these were written by William Henry Channing's mother, Susan Channing, who lived in Brattleboro, Vermont. She reported family events and illnesses, expressed her dismay at her son's letter writing habits, and wrote of her concerns for her son and his family. In a letter dated November 8, 1845, she encouraged William to leave a copy of his papers in a safe place and to consider purchasing a life insurance policy, for which she offered to pay. In an 1847 letter, Susan mentioned the publication of the first volume of Channing's memoirs. In later letters, she described her growing interest in politics and in reading newspapers.
An 1843 letter from J.D. Channing to Susan Channing describes the meetings of a new "church of united brethren and Christian friends," organized in New York by William Russell, at which William H. Channing preached. The letter also mentions Ralph Waldo Emerson's attendance at the meeting and his visit afterwards.
During the Civil War, Channing served as the chaplain of Stanton Hospital. There he received five letters from relatives and friends of deceased soldiers thanking Channing for his kind letters.