General Samuel Cooper was born on June 12, 1798, at New Hackensack, Duchess County, New York, on the Hudson River. At the age of 15, on May 25, 1813, Samuel entered the United States Military Academy at West Point, graduating in a period of two years on December 10, 1815. He finished thirty-sixth in a class of forty graduating with the rank of lieutenant in the light artillery in the United States Army. The period of study at West Point was 2 years at that time, which was later increased to four years of study.
In 1827, at the age of 29, General Cooper married Sarah Maria Mason, a daughter of General John Mason of Clermont, Fairfax County, Virginia. Sarah's grandfather was George Mason.
General Cooper was promoted to First Lieutenant in 1821 and in 1836 was made Captain. During this year, 1836, Samuel wrote the first Concise System of Instructions and Regulations for the Militia and Volunteers of the United States while serving as aide-de-camp, 1828-1836, to major-general Alexander Macomb commanding the army of the United States. This 'works' was later revised and published by Cooper in 1852, by then holding the rank of Colonel. Known as "Cooper's Tactics", it became the standard among the militia and volunteers of the army.
Most of his service, aside from an expedition against the Seminoles in 1841-42, was in Washington. Samuel was selected for staff duty at headquarters of the army, early in his military career. He was appointed an Assistant Adjutant and Inspector General, with the rank of major, in 1838; was made Lieutenant-Colonel in 1847; and was appointed Adjutant and Inspector General of the US Army, with the rank of Colonel, in 1852. These promotions, it is said, were partly a consequence of his highly efficient conduct of business in the War Department during the Mexican War.
The family connections of his wife Sarah, together with a close friendship with Jefferson Davis, which had grown when the latter was Secretary of War, had made him wholly Southern in his feelings and sympathies. This was in spite of his Northern birth and ancestry. At the outbreak of the Civil War, he resigned his commission, March 7, 1861, and went to Montgomery to offer his services to the Confederacy. He was at once made Adjutant and Inspector General of the Confederate army, and was appointed to the full rank of General on August 31, 1861, as soon as that grade was created by Confederate States of America's Congress. He was the senior ranking officer of the Confederate Army throughout the war, reporting only to president Jefferson Davis. Jefferson Davis, in his Rise and Fall of the Confederate Government, reports that the first officers to resign and enlist for the South were Samuel Cooper, Albert Sidney Johnston, and R. E. Lee. Samuel Cooper, as reported by Jefferson Davis, was the first of these to offer his services to the Confederacy at Montgomery.
One of the last official acts of General Cooper, as Adjutant and Inspector General of the United States, was to sign an order of dismissal from the United States army of Brig. General David E. Twiggs, who became a Confederate Major General. That order bears the date of March 1, 1861, and General Cooper's resignation was dated March 7, 1861. His last official act as Adjutant and Inspector General of the Confederacy was turning over the official records of the Confederacy to the United States Government. These records became a valuable contribution to the War of The Rebellion, Official Records of the Union and Confederate Armies. This contribution is said to be Samuel's most lasting contribution to the Confederacy, in overseeing the removal of War Department records from Richmond in April 1865, and protecting them until they could be turned over to Federal authorities in North Carolina after Johnston's surrender.
Unmolested at the end of the war, Samuel returned to find his home, Cameron, near Alexandria had been replaced by a Federal fort. Nevertheless, he moved into what had been an overseer's house, and there took up small farming.
As an aged man living a life as a farmer, General Cooper became a soldier in distress. On August 4, 1870, Robert E. Lee, on behalf of General Lawton, Colonel Cole and others, sent Samuel a sum of money. They were able to raise $300 dollars for Samuel. General Lee in a letter to Samuel wrote "To this sum I have only been able to add $100, but I hope it may enable you to supply some immediate want and prevent you from taxing your strength too much." General Lee also noted in his letter to Samuel, "You must also pardon me for my moving in this matter, and for the foregoing explanation, which I feel obliged to make that you might understand the subject." General Samuel Cooper died on December 3, 1876 at the age of 78 just 6 years after receiving this sum of money. He is laid to rest in Alexandria's Christ Church Cemetery.