Thornton Lakes are located in North Cascades National Park, in the U. S. state of Washington. These paternoster lakes consist of three lakes located southeast of Mount Triumph. Thornton Lakes can be accessed on foot from a trailhead in Ross Lake National Recreation Area. The hike of includes a altitude gain and a descent to Lower Thornton Lake. Two other lakes lie above the first one, unofficially named Middle and Upper Thornton Lakes. A designated backcountry camping zone is located at Lower Thornton Lake.