[Minor edits 12/25/09]
The day after the battle of Cowpens, British commander Lieutenant-Colonel Banastre Tarleton reached the camp of his commander, Major-General Charles Cornwallis. Later that same day, Cornwallis wrote the following report to the British Commander-in-Chief in North America, Henry Clinton.
"Sir: ... General Morgan... [had] by the best accounts I could get... about five hundred men, Continentals & Virginia State Troops, & one hundred Cavalry under Colonel Washington, & six or seven hundred Militia, but that Body is so fluctuating, that it is impossible to ascertain its number, within some hundreds... Lieut. Col. Tarleton conducted his march so well & got so near to General Morgan, who was retreating before him, as to make it dangerous for him to pass the Broad River, and came up with him at 8:00 AM on the 17th instant. Everything now bore the most promising Aspect. The Enemy were drawn up in an open wood and, having been lately joined by some Militia, were more numerous; but the different Quality of the Corps under Lieut. Col. Tarleton's Command, and his great superiority in cavalry, left him no room of doubt of the most brilliant Success. The attack was begun by the first Line of Infantry, consisting of the 7th Regiment, the Infantry of the Legion & Corps of Light Infantry annexed to it; & Troop of Cavalry was placed on each Flank: the 1st Battalion of the 71st, and the Remainder of the Cavalry, formed the reserve. The Enemy's Line soon gave way, & their Militia quitted the Field; but, on our Troops having been thrown in some disorder by the pursuit, General Morgan's Corps faced about & gave them a heavy fire. This unexpected event, occasioned the utmost confusion in the first Line. The 1st Battalion of the 71st & the cavalry were successively ordered up; but neither the exertions, entreaties, or Example of Lieut. Colonel Tarleton could prevent the panic from becoming general; the two three pounders were taken, & I fear the Colors of the seventh Regiment shared the same fate. In justice to the Detachment of the Royal Artillery, I must here observe that no terrors could induce them to abandon their Guns, & they were all either killed or wounded in defense of them. Lieut. Colonel Tarleton with difficulty assembled fifty of his Cavalry, who having had time to recollect themselves, & being animated by the Bravery of the Officer who had so often led them to victory, charged & repulsed Colonel Washington's Horse, retook the Baggage of the Corps, & cut to pieces the detachment of the Enemy who had taken possession of it, & after destroying what they could not conveniently bring off, retired with the Remainder, unmolested, to Hamilton's Ford, near the Mouth of Bullock's Creek. The Loss of our Cavalry is inconsiderable, but I fear, about 400 of the Infantry are either killed or wounded, or taken. I will transmit the particular account of the Loss, as soon as it can be ascertained."
Like Morgan's report, this is one of the most important documents pertaining to the battle of Cowpens. Cornwallis may not have been an eye-witness to the battle, but his account reflects the immediate post-battle views of the most important British participant. Of note is that account is fundamentally similar to Morgan's. The two accounts tend to focus on different details, but they contradict each other on few points. Morgan reported far higher British casualties than Cornwallis admits. Throughout the war, the Americans and British provided different estimates of losses, so this is not unusual. Cornwallis was also writing at a time when it was unclear how many stragglers would make it back to his camp and probably did not wish to overstate his losses. Morgan claimed that he was outnumbered by the British; Cornwallis claimed that Morgan had the numerically superior force. Again, such varying estimates are not unusual. Morgan's report indicates that the 71st was in action with the rest of the infantry before what is known as the 'main line' fight. Cornwallis' report indicates that the 71st was first committed at a later point in the battle.
John Moncure's online history of the battle, The Cowpens Staff Ride and Battlefield Tour, includes a transcription of Cornwallis' report.
Related: Cowpens in Miniature 1, Morgan's Report, Tarleton's Narrative