Correspondence between Katharine Sedgwick Minot and thirty-six friends and family members encompasses the largest part of the Charles Sedgwick papers. Katharine's correspondents include daughter Alice W. Minot; aunt Catharine M. Sedgwick; son Charles Minot; father Charles Sedgwick; mother Elizabeth B. D. Sedgwick; cousin Elizabeth Ellery Sedgwick; aunt Frances Watson; brother-in-law Francis Minot; George Hillard; sister Grace A. S. Ashburner; son Henry Davis Minot; cousin Jane Sedgwick; grandfather Josiah Dwight; friend Julia Hamner; sister-in-law Julia Minot; sister-in-law Louisa Tellkampf Sedgwick; friend Lucy B. Channing; cousin Maria Banyer Sedgwick; cousin Mary Watson; grandmother Rhoda Edwards; son Robert S. Minot; her uncle Robert Sedgwick; friend Sarah Forbes; aunt Susan A. L. Ridley; cousin Theodore Sedgwick III; son William Minot III; husband William Minot II, and brother William D. Sedgwick.

The majority of correspondence is between Katharine and her immediate family members. Correspondence with her daughter, Alice Woodbourne Minot, spans from Alice's childhood (age 7) to adulthood (age 32). Letters written during the Civil War document reaction on the home front from the perspective of a fourteen year old girl. In 1861, she expresses her shock at hearing that Southerners were tying the wounded to trees and noted that her uncle, William D. Sedgwick, had left to fight. In 1862, she refers to a paper signed by the ladies in her town, who have husbands, sons, and brothers at war, to compel the president to remove all incompetent and drunken officers.

Katharine's correspondence with her father, Charles Sedgwick, primarily concerns family events and local news and shows her close relationship with him until his death at age thirty-six. They often wrote to each other when Katharine traveled with her Aunt Kitty (Catharine Maria Sedgwick), Charles' sister, a practice that is later repeated by her own daughter, Alice.

In her correspondence with her mother, Elizabeth B. D. Sedgwick, Katharine confided regularly as she experienced new places, people, marriage and motherhood. In 1842, she describes how, along with her aunt Catharine Maria, she met Charles Dickens at a dinner during his visit to the United States. (This dinner is also documented in correspondence between Charles Sedgwick and William Minot II (see above)).

Letters between Katharine and her mother concerning William D. Sedgwick's letters home illustrate reactions to the Civil War on the home front and how letters from soldiers impacted women back home. Katharine hints about her mother's response to hearing that William has been badly wounded in September 1862.

Most revealing are the letters between Katharine and her husband William Minot II that provide a wealth of information regarding the events related to the Sedgwick and Minot families over several generations. The writings span a forty-year period, from before their marriage in 1842, through Katharine's death in 1880. The letters are often very personal in nature because both travel frequently leaving this as the only means of communication.

For additional correspondence with Katharine Sedgwick Minot see Series VIII General Correspondence. See also Katharine Sedgwick Minot's journals in series IX Bound volumes, diaries and travel journals.

The majority of William D. Sedgwick's correspondence is to his mother, Elizabeth B. D. Sedgwick, during 1861-1862, when he was fighting in the Civil War. In 1861 he was commissioned as first lieutenant in Company D, the 2nd Massachusetts Volunteer Infantry. He was subsequently detailed as ordnance officer of Major-General Nathaniel D. Banks' Corps and was then transferred to the staff of Major-General John Sedgwick with the rank of Major.

William is highly articulate and sets the scene of the Civil War with a high level of detail. He recounts events on the battlefield, military strategy, and the light, weather and ground conditions, as well as what he can smell and hear. He writes, "Dixie, Yankee Doodle and Star Spangled banner have resounded in all directions." On 2 September 1862 he explains that it is his second night without sleep and, "had dismounted for fear of falling out of the saddle and was leaning my head in the horses neck with my arm thrown over him and had just got for a moment fairly asleep, suddenly an explosion occurred."

His letters also reflect the concerns of family at home. In July 1861 he describes his wife Louisa, "having perils and anxieties" and "distressing visions and dreams." He also reveals his father in law's (referred to as the Professor) displeasure at William for fighting. William says that Professor Tellkampf appeals to him to stop and expresses, "the hopelessness of the effort to maintain the union and his consequent disapproval of my continuing in the army." The letters also chart his progression in the army and his aspirations to be part of his cousin John Sedgwick's contingent. This series also contains a certificate of his promotion to assistant adjutant general with the rank of major, signed by Abraham Lincoln in August 1862.

In September 1862, he sent a letter to his mother opening with the words, "I was wounded yesterday." Although he tries to reassure his family that he is fine he later wrote, "my recovery tho' probable is not certain." His mother and sister were with him when he died but his wife did not arrive in time. He died in a farmhouse near the battlefield of Antietam, Maryland, where he had been mortally wounded.

This series also contains condolence letters and other papers related to William's death.