Below this place he built a fort--for it was winter time--and although the natives were not very friendly he collected enough information from them to satisfy himself that he could easily pass down the Illinois to the Mississippi.
He sent one of the Frenchmen, Michel Accault, together with Father Hennepin, to explore the Illinois down to the Mississippi; de Tonty he placed in charge of the fort with a small garrison; and then himself, on the last day of February, 1680, started to walk overland from Lake Michigan to Detroit.

Eventually, by means of a canoe, which he constructed himself, he regained Fort Frontenac and Montreal.

When he returned to Fort Crevecoeur, on the Illinois River,[11] it was to meet with the signs of a horrible disaster.

The Iroquois in his absence had descended on the place with a great war party.

They had massacred the Illinois people dwelling in a big settlement near the fort, and the remains of their mutilated bodies were scattered all over the place.
Their town had been burnt; the fort was empty and abandoned.