Prelude

On December 29, Washington led his army across the Delaware River, and established a defensive position at Trenton.

On December 31, Washington appealed to his men, whose enlistments expired at the end of the year, "Stay for just six more weeks for an extra bounty of ten dollars." His appeal worked, and most of the men agreed to stay. Also, Washington learned that Congress had voted to give him wide-ranging powers for six months

In response to the loss at Trenton, Cornwallis left New York City and reassembled a British force of more than 9,000 at Princeton to oppose Washington.

On January 1, Cornwallis left 1,200 men under the command of Mawhood at Princeton. Cornwallis left Princeton with 8,000 men to attack Washington's army of 6,000 troops. Washington sent troops to skirmish with the approaching British to delay their advance. It was almost nightfall by the time the British reached Trenton. After three failed attempts to cross the bridge over the Assunpink Creek, beyond which were the primary American defenses, Cornwallis called off the attack until the next day.

During the night, Washington called a council-of-war and asked his officers whether they should stand and fight, attempt to cross the river somewhere, or take the back roads to attack Princeton. Although the idea had already occurred to Washington, he learned from Arthur St. Clair and Cadwalader that his plan to attack Princeton was indeed possible. Two intelligence collection efforts, both of which came to fruition at the end of December 1776, supported such a surprise attack. After consulting with his officers, they agreed that the best option was to attack Princeton.

The ground had frozen, making it possible to move the artillery without it sinking into the ground. By midnight, the plan was complete, with the baggage on its way to Burlington and the guns wrapped in heavy cloth to stifle noise and prevent the British from learning of the evacuation. Washington left 500 men behind with two cannon to patrol, keep the fires burning, and to work with picks and shovels to make the British think that they were digging in. Before dawn, these men were to join up with the main army.

By 2:00 AM, the entire army was in motion roughly along Quaker Bridge Road. The men were ordered to march with absolute silence. Along the way, a rumor was spread that they were surrounded and some frightened militiamen fled for Philadelphia. The march was difficult, as some of the route ran through thick woods and it was icy, causing horses to slip, and men to break through ice on ponds.

As dawn came, the army approached a stream called Stony Brook. The road the army took followed Stony Brook for a mile farther until it intersected the Post Road from Trenton to Princeton. However, off to the right of this road, there was an unused road which crossed the farmland of Thomas Clark. The road was not visible from the Post Road, and ran through cleared land to a stretch from which the town could be entered at any point because the British had left it undefended.

However, Washington was running behind schedule as he had planned to attack and capture the British outposts before dawn and capture the garrison shortly afterward. By the time dawn broke, he was still two miles from the town. Washington sent 350 men under the command of Mercer to destroy the bridge over Stony Creek in order to delay Cornwallis's army when he found out that Washington had escaped.

Shortly before 8:00 AM, Washington wheeled the rest of the army to the right down the unused road. First in the column went Sullivan's division consisting of St. Clair's and Isaac Sherman's brigades. Following them were Cadwalader's brigade and then Daniel Hitchcock's.

Cornwallis had sent orders to Mawhood to bring the 17th and 55th British regiments to join his army in the morning. Mawhood had moved out from Princeton to fulfill these orders when his troops climbed the hill south of Stony Brook and sighted the main American army. Unable to figure out the size of the American army due to the wooded hills, he sent a rider to warn the 40th British Regiment, which he had left in Princeton, then wheeled the 17th and 55th Regiments around and headed back to Princeton. That day, Mawhood had called off the patrol which was to reconnoiter the area from which Washington was approaching.

Mercer received word that Mawhood was leading his troops back across the bridge and back to Princeton. Mercer, on orders from Washington, moved his column to the right in order to hit the British before they could confront Washington's main army. Mercer moved towards Mawhood's rear but when he realized he would not be able to cut off Mawhood in time, he decided to join Sullivan. When Mawhood learned that Mercer was in his rear and moving to join Sullivan, Mawhood detached part of the 55th Regiment to join the 40th Regiment in the town and then moved the rest of the 55th, the 17th, fifty cavalry, and two artillery pieces to attack Mercer.