Cornwallis waited in vain for a rescue. In September he had written Clinton, “This place is in no State of defence. If you cannot relieve me very soon, you must be prepared to hear the Worst.” Clinton was aware of the stakes, but he did not move quickly enough. He set sail for the Chesapeake on October 19 with twenty five ships of the line and 7,000 soldiers. When he arrived off the Chesapeake on October 24, he learned that Yorktown had fallen the day he left New York.

With his situation desperate, Cornwallis attempted to strike back. Before dawn on October 16, he sent 350 men in a sortie against two newly erected batteries in the allied line. The British penetrated the works and spiked a few guns with bayonet points before a counterattack by French grenadiers drove them back. Eight of the British were killed and twelve taken prisoner. The French suffered twenty casualties. The raid had no serious effect on the siege. Within a few hours the spiked guns were repaired and joined in the bombardment of Yorktown.

That night, Cornwallis tried to open an avenue of escape. He and a third of his army rowed across the York River to Gloucester. He planned to attack and force his way past the blockading force. Once in the open, he would make a dash across country toward the security of Clinton's army in the north. A storm suddenly blew up and scattered his small fleet of boats. This and the strength of the American lines took the fight out of Cornwallis. The next day the boats were retrieved and the men rowed back across the river.

In Yorktown, the British position had become untenable. The allied bombardment was knocking the remaining British fortifications to pieces. The defenders could not mount a gun. Ammunition was running low. Cornwallis gave in to the inevitable.

On the morning of the October 17, the British raised a white flag. Gradually the allied bombardment halted. A drummer emerged from the British trenches, beating a parley. He was followed by an officer bearing a white flag. This began the process of negotiating the British surrender. Cornwallis hoped to have his army sent back to Britain on parole, but Washington refused to allow this. The men in Cornwallis's army would become prisoners of war. In the interests of getting a speedy surrender, Washington allowed Cornwallis to send a ship with dispatches to Clinton in New York. He knew this ship would be loaded with loyalists wanted by the American authorities.

The articles of surrender were signed on October 19. At two o'clock that afternoon, the British army marched out of Yorktown to lay down their arms. They paraded between two lines of allied troops, the French on their left and the Americans on their right. General Cornwallis stayed away from the surrender ceremony, sending word that he was ill. Brigadier General Charles O'Hara was obliged to formally surrender the British army. O'Hara tried to surrender to Rochambeau, but was told that he had to surrender to Washington. When O'Hara offered his sword to the American commander in chief, Washington directed him to General Benjamin Lincoln. Lincoln took the sword and immediately returned it. As O'Hara rode away “tears rolled down his cheeks.”

For the British, Yorktown was the climactic disaster of a war effort gone wrong. The allies took 7,247 soldiers and 840 sailors prisoner. Along with the prisoners, the allies captured 244 cannon and a great quantity of military stores. During the siege of Yorktown, Americans casualties were twenty killed and fifty-six wounded, French casualties were fifty-two killed and 136 wounded, and British casualties were 156 killed and 326 wounded.