Prairie du Rocher ("The Rock Prairie" in French) is a village in Randolph County, Illinois, United States. Founded in the French colonial period in the American Midwest, the community is located near bluffs that flank the east side of the Mississippi River along the floodplain often called the "American Bottom". The population was 502 at the 2020 census. Prairie du Rocher is one of the oldest communities in the 21st century United States that was founded as a French settlement. About four miles to the west, closer to the Mississippi River, is Fort de Chartres, site of a French military fortification and colonial headquarters established in 1720. Some buildings were reconstructed after falling into ruins, and the complex is now a state park and historical site. The fort and town were a center of government and commerce at the time when France claimed a vast territory in North America, New France or La Louisiane, which stretched from present-day Louisiana and the Illinois Country to Canada. The village was founded in 1722 by French colonists, mostly migrants from Canada. History New France In 1718, Pierre Dugué de Boisbriand built the first Fort de Chartres. In 1722, St. Thérèse Langlois, a nephew of Boisbriand, founded Prairie du Rocher. The town was built on a tract of land donated by the Royal Indian Company. Boisbriand later became the commandant of the area. The town was strategically located along fertile Mississippi River bottomland. Surpluses from the productive cultivation by habitants later helped supply critical wheat and corn to New Orleans and other lower Louisiana Territory communities. D'Artaguette, an inspector in the country in the early 18th century, wrote: This country is one of the most beautiful in all Louisiana. Every kind of grain and vegetables are produced here in the greatest abundance .... they have, also, large numbers of oxen, cows, sheep, etc., upon the prairies. Poultry is abundant, and fish plentiful. So that, in fact, they lack none of the necessaries or conveniences of life. In 1743 the territorial government granted the Prairie du Rocher Common (land used by all the villagers) to the village; the common was used until 1852. The villagers had plots for cultivation defined in typical French fashion: long narrow lots that reached back from the riverfront through the common. The villagers kept the plots open within the common, and built a fence around it to keep out livestock.