Approximately 12,000 American soldiers wintered at Valley Forge in 1777–78.
George Washington led the Continental Army into the Pennsylvania encampment on December 19, 1777, after British forces captured Philadelphia. Valley Forge was about 18 miles northwest of the city, close enough to monitor British movements but positioned on defensible high ground between Philadelphia and the Continental Congress at York.
The encampment lasted until June 19, 1778. The army faced severe shortages of food, clothing, shoes, and medicine, made worse by poor roads, supply failures, and a weak procurement system. Disease and malnutrition killed roughly 1,700 to 2,000 troops, most in hospitals outside the main camp. The famous story is therefore about hardship, but not about an army of only a few thousand men.
The approximately 12,000 figure includes the people who accompanied the army, including soldiers, artisans, women, and children; estimates can vary depending on who is counted. Valley Forge also became a place of military reform. Baron Friedrich von Steuben helped impose more systematic drilling and discipline, strengthening the army before the 1778 Battle of Monmouth.