North of its intersection with Blue Mountain Road and Pryor Road, US 15 leaves the park boundary and enters the town of Thurmont. The U.S. Highway has a diamond interchange with unnamed and unsigned MD 15C that leads to the northern end of MD 806 and to Frederick Road, which serves a commercial area south of downtown Thurmont. US 15 continues north to a folded diamond interchange with MD 77 (Main Street) where the highway also crosses Hunting Creek; MD 77 follows the creek up the mountain as Foxville Road toward Catoctin Mountain Park. The highway intersects Sandy Spring Lane (unsigned MD 15D) and crosses over the Maryland Midland Railway. US 15 leaves the town of Thurmont and meets MD 550 (Church Street) at a diamond interchange before crossing Owens Creek, which MD 550 follows up the mountain as Sabillasville Road. The U.S. Highway heads northeast through farmland and meets the northern end of MD 76 (Motters Station Road) before bisecting the campus of Mount St. Mary's University. The main part of the campus and National Shrine Grotto of Our Lady of Lourdes are located to the west of the highway; the athletic complex, which includes Knott Arena, is to the east.