When news of Clark's actions reached Fort Detroit, British Lt. Governor Henry Hamilton decided to march south with a small force of men which included some French volunteers still loyal to England. He was joined along the way by hundreds of Indians who had also remained loyal to the British. Upon arrival at Fort Sackville in Vincennes, he easily impressed the French with his great force of men and convinced them to renounce their new American alliance. The American commander in charge, Captain Leonard Helm, was left with no choice but to surrender the fort on December 17, 1778.
George Rogers Clark was in the far western Illinois Country, and he had no idea that Hamilton had moved south from Detroit or that the American forces in Vincennes had been overwhelmed. Neither did a merchant named Francis Vigo who was sent by Clark to travel to Vincennes. Vigo was well known to be sympathetic to the American cause, so when he came through Vincennes unaware that the British were now in control, he was taken prisoner by Hamilton. Vigo was able to convince Hamilton that he was no threat. Hamilton agreed to let Vigo travel straight back to St. Louis, as long as Vigo did not deviate along the way to warn Clark about the situation at Fort Sackville. Vigo kept his word, but then immediately upon reaching St. Louis, turned south to Kaskaskia and revealed to Clark Hamilton's position and strength. There is a statue of Francis Vigo located outside between the Memorial and the Wabash River.
Clark knew his small force of frontiersmen could not succeed in the taking of Fort Sackville once spring arrived and Hamilton's Indian allies returned to Vincennes from their winter homes. Clark's only hope of taking the fort lay in a surprise midwinter attack. Clark set out with approximately 170 of his men and began a 160 mile trek across the freezing plains of southern Illinois. A midwinter thaw had set in, causing a torrent of water to come down from the north. This meant that the last 10 days of this 19 day journey were spent in icy cold water that at times reached the men's necks. Finally, on February 23, Clark and his men arrived at Fort Sackville.