On 1 Jan 1718, John Law and his Company of the West was granted a trade monopoly. Planning to make a fortune mining precious metals, they built a fort to protect their interests. The original wooden fort was built between 1718 -1720. When administration of Illinois Country transferred from Canada to New Orleans, the fort became the seat of governance. It was also meant to control Natives in the area, particularly the Fox. The original fort was a palisade of logs with two bastions at opposite corners.
Built on the flood plain of the Mississippi, the fort quickly deteriorated. Construction of a second fort, further from the river, but still on the flood plan began in 1725. This fort was also made of logs, but had a bastion at each corner. The second wood fort didn't deteriorate quite as fast, but by 1742 was in bad repair.
In 1747, the French garrison moved to the primary settlement in the region 18 miles south to Kaskaskia. The French debated whether to rebuild the fort. Officials in New Orleans were in favor of building a new fort at Kaskaskia, but the local commandant argued for a place closer to the original fort. Ultimately, the government decided to build a stone fort near the original fort site. Construction began on the fort in 1753. Although it was mostly finished by 1756, construction still continued until 1760. The stone was quarried in the bluffs nearby and ferried across a lake to the construction site. The limestone fort had walls fifteen feet high and three feet thick. Approximately four acres was encompassed in the fort.
With the Treaty of Paris, the British acquired Illinois Country. However it wasn't until 10 Oct 1765 that the 42nd Royal Highland Regiment took control of the fort. Frenchmen in the area were ordered to leave or obtain a special license to remain. Many moved to St Louis, with it's more congenial culture. The fort was then renamed Fort Cavendish.
Powder Magazine before restoration
The British saw little value in the post and abandoned it in 1771. After it was abandoned, the river took it's toll. In 1772, the south bastion and wall fell into the river. By 1820, it was noted that trees were growing from the walls. Locals carried off stone from the walls for their own construction projects. By 1900, the walls were gone and the only structure remaining was the stone building used as a powder magazine.
The State of Illinois acquired the property in 1913. They restored the powder magazine in 1917. In the 1920s, the foundations were exposed. In the 1930s, the front wall and gatehouse were reconstructed. Today the site is a museum celebrating French Colonial life in 18th century Illinois.