After the fighting the inconclusive Battle of White Marsh on 5-8 December 1777, General Washington began looking for a suitable winter encampment that would allow him to keep an eye on Lt. Gen. Sir Henry Clinton’s army in Philadelphia. The 12,000 Continental troops in Washington’s army soon established a camp at Valley Forge, some eighteen miles northwest of Philadelphia.
"The General ardently wishes, it were now in his power, to conduct the troops into the best winter quarters....With activity and diligence Huts may be erected that will be warm and dry—In these the troops will be compact, more secure against surprises than if in a divided state and at hand to protect the country. These cogent reasons have determined the General to take post in the neighbourhood of this camp....Tomorrow being the day set apart by the Honorable Congress for public Thanksgiving and Praise....The General directs that the army remain in it’s present quarters, and that the Chaplains perform divine service with their several Corps and brigades."
Gen. George Washington, General Orders, 17 December 1777www.founders.archives.gov