The Jenny Lake trail follows the outline of Jenny lake for the entire circumference. The first two miles are shared with Cascade Canyon Trail, and it breaks off as Cascade Canyon Trail turns up the canyon to Hidden Falls. Jenny Lake trail continues around the remainder of the lake, including crossing the River between Jenny Lake and String Lake with a branch trail proceeding to String Lake.
From Jackson WY, proceed North through Grand Teton National Park. At Moose Junction, turn left and proceed west to the park entrance. At Jenny Lake junction, follow the signs to Jenny Lake Visitor Center and boat docks. Trailhead is located adjacent to the boat docks.
http://www.tripleblaze.com/trail.php?c=3&i=2147