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.