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("Prairie of the Rock" 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 in the floodplain often called the "American Bottom".
Prairie du Rocher is one of the oldest communities founded as a French settlement that survives in the 21st century. The nearby Fort de Chartres, site of a French military fortification and colonial headquarters established in 1720, 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, which stretched from Louisiana and the Illinois Country to Canada.
The population was 613 at the 2000 census. It was founded in 1722 by French colonists.
Prairie du Rocher is located at (38.081755, -90.096243). It is approximately 40 miles south of St. Louis, Missouri. It has an elevation of 396 feet above sea-level and is situated underneath the Mississippi River bluffs. It is located approximately 4 miles east of the Mississippi River.
According to the United States Census Bureau, the village has a total area of 0.6 square miles (1.5 km²), all of it land.
Illinois Route 155 is the only state highway that runs through Prairie du Rocher. It connects the town with Ruma, Illinois, 7 miles to the northeast and Fort de Chartres, 4 miles to the west. Several other smaller roads connect it to various other surrounding communities.