Burgoyne marched seven miles down the Hudson to Fort Miller, an abandoned trading post. Here he was immobilized until September 13. Burgoyne's logistical situation was growing increasingly serious. He needed to draw supplies from the local area, but these were not to be had. As a practical matter, Albany was growing more distant.

Lieutenant Colonel Barry St. Leger commanded the column that was to support Burgoyne by advancing on Albany from the west along the Mohawk Valley. St. Leger left Oswego on July 26. He had with him a mixed force of 875 redcoats, Hessian jaegers, and loyalists. Joseph Brant, the Mohawk chieftain, joined him with 1,000 Indians.

The only obstacle on St. Leger's path through the Mohawk Valley was Fort Stanwix, garrisoned by 750 Continentals and militia commanded by Colonel Peter Gansevoort and Lieutenant Colonel Marinus Willett. St. Leger arrived at Fort Stanwix on August 2. After a parade of his force failed to intimidate the garrison into surrender, St. Leger settled down for a siege. He sent many of his European troops back to bring up his artillery and to collect supplies.

Hearing of St. Leger's arrival, General Nicholas Herkimer organized a relief force of 800 militia. Aware of their approach on August 6, St. Leger sent a force of 400 loyalists and Indians to intercept them. Despite Oneida Indian scouts, Herkimer's militia walked into an ambush in some ravines near Oriskany. The militia formed a circle and fought back desperately. Wounded in the leg, Herkimer directed his men to prop him up against a tree. The fighting was often hand-to-hand.

Given the size of the combatant forces, Oriskany was one of the bloodiest battles of the Revolutionary War. Suffering heavy casualties, the Indians fell back. The badly shaken militia withdrew as well. The militia lost 150 to 200 dead. More than fifty men were wounded, including General Herkimer, who died after his leg was amputated. Several men were captured and later tortured to death by the Indians. The loyalists and Indians lost around 150 men, an especially severe blow to the Indians, who could not afford many casualties.

While the fighting was going on at Oriskany, Colonel Gansevoort sent Willett and 250 men to raid St. Leger's camp. Easily driving off the guard, Willett collected twenty-one wagonloads of equipment and supplies. The loss of their goods further soured the mood of the Indians. St. Leger tried to use their rage as a weapon, threatening the garrison of Fort Stanwix with a massacre if they did not surrender. Gansevoort responded by sending Willett to find help. Willett found it in the form of a relief column of 1,000 men dispatched by General Schuyler and commanded by Benedict Arnold. Arnold hastened St. Leger's departure by sending ahead a captured loyalist with the tale that he was coming at the head of 3,000 men. This threw St. Leger's camp into turmoil. The Indians began leaving en masse. St. Leger was forced to retreat to Oswego. Burgoyne would get no assistance from him.

By August, Burgoyne badly needed draft animals to help transport his army to Albany. He still hoped to bring with him a fifty-two-gun artillery train, in addition to supplies and equipment for his infantry. Since the local population was not stepping forward to assist him, he had to look farther afield. Baron von Riedesel heard that horses were plentiful in the Connecticut River Valley. Burgoyne agreed to send an expedition into New England. He optimistically expected to collect cattle, wagons, and 1,300 horses. A loyalist informed Burgoyne that large amounts of flour and many horses could be had at Bennington, Vermont. On August 11, a mixed force of Hessians, loyalists, Canadians, Indians, dismounted dragoons, and a German band — in all 650 men — set off for Bennington. Commanding the column was Lieutenant Colonel Friedrich Baum, a Hessian officer who could not speak English.

The people of Vermont had just declared themselves an independent state. Worried about the impending threat from Burgoyne, they called for help from the neighboring New England states. New Hampshire responded by raising a brigade of 1,500 men. Commanding this force was John Stark, who had fought with Roger's Rangers during the French and Indian War, and who had served with distinction at Bunker Hill, Trenton, and Princeton. Stark marched to Bennington, joining 500 militiamen already gathered at the village. He was there when word came that Indians were in the area. Baum's Indian auxiliaries had moved ahead of the main force and were looting and killing cattle for their bells, imprudently alarming the countryside.

Once Stark realized that Baum's force was on the way, he called for help. Colonel Seth Warner headed down from Manchester with 350 Continentals. Baum and Stark confronted each other on August 14. Neither felt strong enough to attack. Baum fortified himself on a hill and sent for help. Some ninety loyalists reinforced him. Rain prevented action on August 15. The next day, Stark and Warner attacked. The loyalists and Indians ran away. The Hessians were overwhelmed. The survivors surrendered when Baum was mortally wounded. The Americans gave themselves over to looting Baum's camp. At this point a relief force of 650 Hessians under Lieutenant Colonel Francis Breymann approached. Stark and Warner scrambled to assemble a force to meet this threat, then swarmed over the advancing Hessians. In fighting that resembled the Battle of Concord, the relief column was routed. Only darkness gave Breymann a chance to get away. More than 200 Hessians were killed in the fighting and 700 were captured. The Americans suffered thirty dead and forty wounded.