From 1720-1763, the French administration of the Illinois Country was centered at the forts, which were built successively over a 40 year period on or near the same site.
The fort was originally constructed in wood on the Mississippi River, 18 miles north of Kaskaskia. The French officials in New Orleans sent a contingent of army officers, government officials, company employees, mining engineers, workmen and soldiers to establish a civil government in the Illinois country. It was also hoped that a military presence would pacify the Fox Indians, whose frequent attacks put great pressure on French villages.
The original fort consisted of a palisade of squared logs surrounded by a dry moat. Bastions built at diagonally opposite corners provided cover fire for each wall. Several buildings occupied the interior, including the Provincial Council building which conducted the affairs of the King and Company. The original fort, subject to frequent flooding, deteriorated rapidly.
A new fort was begun about 1725. It was built of logs and was located farther inland from the Mississippi River than before. By 1742, however, this fort's condition was in such a state of disrepair that the garrison once again moved the fort, this time to Kaskaskia.
A stone Fort de Chartres was built in 1760. It was surrendered 10 years later to Great Britain in the 1763 Treaty of Paris that ended the Seven Years War. On October 10, 1765, in a carefully choreographed transfer ceremony, the Black Watch Scottish Highlanders marched in with their kilts and bagpipes and wrested control of Fort de Chartres and the French Colonial District.
The British renamed the fort to Fort Cavendish, but in all they really made little use of the fort they now possessed. Military engineers tried to control the erosion caused by the Mississippi River, but the British military leaders in North America soon deemed the fort of little practical value and abandoned it in 1771, ending its use as a military post.