Before the Continental Army arrived, Valley Forge was a small industrial and agricultural community along Valley Creek and the Schuylkill River. Quaker entrepreneurs established an iron forge there in the 1740s, and the Potts family expanded mills, dwellings, and related works. British forces raided the industrial site during the 1777 Philadelphia campaign. After defeats at Brandywine and Germantown and the British occupation of Philadelphia, George Washington selected the defensible upland nearby for the army's third winter encampment.

The army marched into Valley Forge on December 19, 1777. Roughly 12,000 soldiers and hundreds of women and children created a temporary military city, constructing thousands of log huts along planned brigade streets. Washington used Isaac Potts's house as headquarters. The camp protected Congress and supply routes while keeping pressure on British-held Philadelphia. Its location also made provisioning difficult, and transportation failures, currency depreciation, corruption, and competition among military and civilian buyers contributed to recurring shortages.

Popular memory often portrays Valley Forge as a single winter of starvation and snow, but conditions changed over six months. Food, clothing, and shelter were unevenly distributed, and disease ultimately killed more people than exposure. Smallpox inoculation, sanitation measures, and improvements in supply reduced some dangers. Camp life depended on soldiers from many states, Indigenous allies, free and enslaved Black men, women who cooked and laundered, artisans, teamsters, sutlers, and local civilians whose property and labor were drawn into the encampment.

Friedrich Wilhelm von Steuben arrived in February 1778 and introduced a more consistent system of drill, maneuver, camp administration, and inspection. His instruction strengthened coordination without creating the army from nothing. The alliance with France, announced in May, raised morale and changed the strategic situation. When British forces evacuated Philadelphia, the Continental Army left Valley Forge on June 19, 1778, crossed the Delaware River, and fought at Monmouth later that month. The encampment became associated with endurance, reform, and national perseverance.

Veterans, descendants, and civic groups began memorializing Valley Forge during the nineteenth century. Pennsylvania created Valley Forge State Park in 1893, protecting land, erecting monuments, reconstructing huts, and reshaping the landscape according to contemporary commemorative ideas. The National Memorial Arch was dedicated in 1917 as a focal point for public remembrance. Congress authorized Valley Forge National Historical Park in 1976, and Pennsylvania transferred the property to the federal government. Current interpretation combines military history with archaeology, environment, industry, civilian displacement, race, labor, and the complicated history of preservation itself.