First Lieutenant 2d Mass. Vols. (Infantry), May 25, 1861; Major and A. A. G. U. S. Vols., September 16, 186; died at Keedysville, Md., September 29, 1862, of a wound received at Antietam, September 17.
William Dwight Sedgwick was the only son of Charles and Elizabeth (Dwight) Sedgwick, and was born in Lenox, Massachusetts, June 27, 1831. Till the age of fourteen years he was brought up almost entirely at home, when his father sent him to Illinois to spend a summer with a farmer who was a relative, and who then lived in a log-house. Here he learned and performed every kind of farm-work of which a boy of that age is capable, and confirmed a constitution originally excellent. His father believed that, without some personal knowledge and experience of labor, he could not have a proper sympathy with laboring men. He spend one year at a French school, and one in a boys' school taught by Rev. Samuel P. Parker, in Stockbridge, Massachusetts, and finished in Lenox his studies preparatory to admission into college. After leaving college, he spent one winter in a law-office; then went abroad and studied a portion of his profession at Heidelberg, Gottingen, and Breslau. He was abroad about seventeen months. After his return, he entered the Cambrdge Law School, where he remained a year, and then established himself as a lawyer in St. Louis, Missouri. It was his good fortune to grow up, through all his boyhood and the greater part of his youth, under the eye of two excellent parents, both remarkably gifted. He was allowed to develop with great freedom and under the happiest influences and circumstances. The fear of disobeying and displeasing them was almost the only restraint he knew; and he was so accustomed to give his parents his full confidence, that, even as a young man and away from them, he never tried or wished  to hide his faults, and always found in their forbearance and assistance the surest help to overcome them. His happy natural tendencies were carefully cultivated and strengthened, and the truthfulness, humanity, and kindness to every living being, which were the characteristics of both parents, and which he saw daily and hourly practised in his father's house, became also his second nature. From his mother he inherited the happiest temper, great sweetness and cheerfulness, with great natural courage and firmness combined and from his father the refinement of sentiment, the keen enjoyment of wit and fun, and some portion of that pleasant humor for which his father's conversation is still remembered with delight by those who knew him. The free and extensive hospitality of his parents, and the attraction which the society of his aunt, Miss C. M. Sedgwick, added to the family circle, brought among the many guests a large number of distinguished and superior people into the house; and William Sedgwick enjoyed the opportunity, rare for a boy and young man, of seeing, in a perfectly unconstrained way, the best society, and of acquiring early that ease and quiet self-possession, and the winning manners, which marked him at once as the gentleman wherever he appeared. No wonder that his happy home seemed perfect to him, and his birthplace the loveliest spot on earth. His love for it became only strengthened by separation; and even with the grandeur of the Alps before him, even in Rome, he could sigh for the beauties of his own mountains, lakes, and valleys. He had great love for and enjoyment in nature, and had gained much skill in all rural and manly exercises and amusements, which were so peculiarly adapted to his taste and his strong, robust constitution, that afterwards in town-life and amid sedentary occupations he often painfully longed for them. While no amount of fatigue, of hardship, or privations, could subdue his spirits or disturb his good humor, he was yet liable to become depressed by the confinement of his life as a lawyer. With these decided tastes for out-door life and occupations, it seems but natural that the temptation to neglect his books and  studies for the delight of following them proved sometimes too strong for an active and spirited young man; but his natural capacities and talents were such, that, had he really lost anything by these interruptions, he very easily could repair the want by a few hours' earnest study, where others had to give at least double the time. Though originally he had no very strong preference for his profession, he had always regarded it as a noble and interesting one. With all his advantages at home and abroad, he had been carefully and excellently prepared for it, and in some respects was peculiarly fitted to become a distinguished member of the bar. He spoke as well and as clearly as he wrote, had a sound and excellent judgment, a lively imagination, great self-possession and readiness; and even a certain pertinacity—of which he often accused himself as a great fault, and which among his friends made him almost always carry his point—seemed only the better to qualify him for a lawyer. The few years in St. Louis were prosperous for him, and very promising for the future; and no doubt he would have continued in his profession, and would have done honor to it, had not, from the moment of the outbreak of the war, the destiny of his country occupied his mind so powerfully that only with difficulty could he turn his thoughts to other matters. He felt irresistibly drawn to become active in the great national struggle; and this last year and a half of his life, with all its new and most interesting, but often sad and terrible, experiences, did much to ripen and elevate his character. He married, in 1857, at Hanover, in Germany, Louisa Frederica Tellkampf, daughter of Professor A. Tellkampf of that place. From his letters to his father-in-law at the beginning of the war we can best learn the earnest and intense interest which he took in the destiny of his people, and the motives that decided him to leave his profession and family to offer his services to the country. In reply to the warning of Professor Tellkampf, not to engage himself in the war, and before the former knew that he had joined the army already, he says:— 
Your views are perfectly natural; but the same reasons which should induce me to withdraw from the service of government would, if adopted by all those to whom they apply as well as to me, break up our armies and leave us at the mercy of Southern dictators. In one prediction I have seen already that I was quite right, —in saying to my friends, when they tried to persuade me to the contrary, that we should find there would be far from a superabundance of those ready for their country's call to arms, and that every one would be needed; even now we have barely enough to stand on the defensive. After having once taken the step, and feeling as I do, I know you could only despise me, should I forsake my country's cause because you regard it as almost hopeless. Were these views, which I believe are general, not only in Germany but in all Europe, to prevail throughout the North, and were those engaged now in their country's service to reason as foreigners do for us, we should be lost indeed; but we should deserve our fate, in such a case, and for very shame could only wish to be buried in the ruins our want of faith had involved us in. For my part, if my country is to perish, my hope is to perish with her. I could not wish to survive the downfall of what I regard as the world's hope. Should America cease to be a first-class power, and be broken up in contemptible little fragments, what would you think would become of England? How long would it be before she would lie before the feet of France? What would become of the surplus population of Europe? What chance would be left to Germany and Italy in the struggle for eventual freedom after the failure of the grandest experiment of a free government that the world has known? Utter discouragement and dejection would fall upon the friends of freedom everywhere, should the North now yield to the entreaties of those who say, “Do not persist in this war, for you will be only shedding blood to no purpose.”In accordance with these principles, Mr. Sedgwick forsook his profession, and was commissioned (May 25, 1861) as First Lieutenant in the Second Massachusetts Volunteers (Colonel Gordon). He went into service with the regiment, was detailed as ordnance officer of Major-General Banks's corps, and was soon transferred to the staff of Major-General Sedgwick, his kinsman, with the rank of Major. All through his period of service he wrote constantly to his family; and the following extracts will show his habits of mind, and the spirit in which he served his country. 
In another letter, written to his father-in-law in January, 1862, he says:—
These few extracts from his letters can only serve to show what he was as a patriot, how clear and sound and good his judgment, and how well, even in the beginning of the war, and  in some of the darkest times of it, he foresaw with the eyes of his spirit the triumph of his country, which he was not destined to share. His letters, of which there remain a large number, seem to preserve to his friends a living part of him, and have the great charm of giving always a true and striking portrait of the mood and moment in which they were written. Many are overflowing with pleasantry and humor,—all with the tenderness and kindness of his heart. Some show an uncommon talent for the description of nature, as well as for the delineation of character; and his way of expressing himself is always happy, clear, and natural. In these, written to his most intimate friends, he freely gives his religious sentiments, his views of life and destiny; and all he says is pervaded by the generous and noble spirit from which it flows. In his military career, he found a great advantage in having formerly hardened and disciplined his body by all manly exercises, so that he was better prepared for the great exposure and fatigue that broke down many delicate constitutions. Great physical courage seemed born with him, and was so natural that he never knew the nervousness and timidity of more sensitive natures, but it helped him, no doubt, to acquire that higher moral courage which acts independently of the judgment, the approval or blame of others, and which has as its aim only that which the mind has once recognized as right and duty. He thought so little what others might think or say of him, that his actions never seemed influenced by it; and he not only appeared always perfectly natural, self-possessed, and without restraint himself, but had also the happy gift to take restraint and reserve from others, and to awaken confidence, kind feelings, and good humor. He soon became therefore, popular among his fellow-officers and his inferiors, as he had been always where he lived. His personal appearance was prepossessing, his figure tall and strongly built, and his face well expressed his character. It was at once a very manly and a very sweet face, with dark, expressive eyes, and handsome, regular features; and the refinement, the inborn nobility of his soul, and the high idea to which he devoted the end of his life, had set their stamp upon  it. In his military service, his duties were always promptly and cheerfully fulfilled; and camp life, which throws men and officers so intimately together, gave him many opportunities to do kind offices to others. His firmness and gentleness made him also a desirable assistant when amputations and difficult operations among the wounded were to be performed. He had formerly, in the universities, steeled his nerves by witnessing such painful scenes, after he once found he was very weak in looking at the sufferings of others, and needed some self-discipline to acquire that perfect composure which he thought every man ought to have. How quietly and manfully he bore his pain his own words show (written in his diary), when he lay in the great agony of his mortal wound on the battle-field of Antietam.
While trying to rally our men, a musket-ball struck me in the small of my back, and I fell from my horse. As I write this, I have been lying here more than an hour, powerless to move my right leg. I think the wound must be mortal. I have been praying God to forgive my sins, to bless and comfort my darling wife and children, my dearest mother and sisters. As I have been lying here in very great pain, shells have been bursting close to me almost constantly. I wish my friends to know that I have fallen while doing my duty as well as was possible, which I can truly assert, and that I have not uttered a groan as yet, lying alone on the hard ground, in the sun, with no friend near.Eight hours he remained in this same position, till found by his friends. He was carried into a farm-house, where he received the kindest treatment. His mother and sister had the consolation of being with him during his last sickness, and present at his death; not so his wife, who learned her misfortune only at the moment of her arrival from Europe. He left behind him three little girls, the youngest of whom he had never seen. He probably little thought, when he wrote, two days before the battle of Antietam, in a letter which alludes to the want of sleep he had undergone, ‘O, how I long for a few hours' assured rest!’ how soon his eyes should close in the last deepest sleep, from which there is no more awakening. Many were the hearts that mourned his death, and many the tears that were shed at his early grave.