Fort Defiance, known as Camp Defiance during the American Civil War, is a former military fortification located at the confluence of the Ohio and Mississippi rivers near Cairo in Alexander County, Illinois. The strategic significance of the site has been known since prehistoric times with archaeological evidence of warfare dating to the Mississippian era. It is the southernmost point in the state of Illinois. Fort Defiance Park, formerly a State Park, is owned and maintained by the city of Cairo. At 279 feet (85 m) elevation, Fort Defiance Point is Illinois' lowest point.