The event in which Fort Massac played a part, which was to have the greatest influence in its section, took place, however, not during its French and Indian days, but later, when the American colonies were asserting their independence of the Mother Country. All of the Illinois country was held then by His Majesty’s troops, but it was common information that the French inhabitants of the conquered country were not extraordinarily well disposed to their rulers and that the garrisons of the English strongholds here had been largely reduced to aid the fight on the eastern sea-coast. Accordingly it entered the head of one George Rogers Clark, a daring borderman of twenty-six years, Virginian by birth, that it would not be an impossible task to take from the English by force the country which they had in this manner seized from the French. June, 1778, saw him landing at Fort Massac, then ungarrisoned, with a small body of men, and this same day probably saw the American flag unfurled for the first time west of the Ohio River, as it is confidently believed that Clark brought a copy of the new standard with him. From Fort Massac the expedition set out and achieved the ends which its commander forevisioned with many deeds of daring. It opened the gates to American settlement of all the northwest country of the United States.
Fort Massac was not occupied by troops until 1794, when, in view of probable collision with Spain and France, Washington despatched Major Thomas Doyle, of the United States Army, to rebuild and occupy the post. This was done and for some years it was of importance. In 1797 about thirty families had settled in the neighborhood, Captain Zebulon Pike being in command of a garrison of eighty-three men. At different times General Anthony Wayne and James Wilkinson occupied the fort as their head-quarters. In 1812 it was garrisoned by a Tennessee volunteer regiment, but at the close of that conflict the fort was evacuated once more.
In 1855, according to an account of Governor Reynolds, of Illinois, Fort Massac was in good condition. The walls, 135 feet square, were strong and at each corner was a stout bastion. A large well of sweet water was within the fortress and the walls were palisaded with earth between the wood.