Jacks Knob is a 3,813-foot mountain in northern Georgia on the border of Towns and Union counties, in the Mark Trail Wilderness of the Chattahoochee National Forest. Set in a high, heavily wooded section of the Blue Ridge, it is part of a landscape crossed by important mountain trails. The Appalachian Trail runs along the mountain’s southern flank, and the Jacks Knob Trail ends here where it joins that long-distance route. At the mountain’s southeastern foot, in Jacks Gap, lies the source of the Chattahoochee River in the far southeastern corner of Union County.