MD 42 begins at a tangent intersection with US 219 at the northern edge of McHenry near Deep Creek Lake. The state highway heads north as a two-lane undivided road. After meeting Hoyes Sang Run Road in the hamlet of Hoyes, MD 42 curves west then north again through farmland. The state highway features a pull-off for trucks to check their brakes before starting a descent with grades of up to 8%. The uphill direction has a climbing lane for part of the ascent. At the bottom of the hill, MD 42 enters the town of Friendsville and turns west. First Avenue, which is unsignedMD 742, heads north into the center of Friendsville while MD 42 bypasses the town center to the south and west. After crossing the Youghiogheny River, MD 42 turns northwest and meets Interstate 68 at a diamond interchange. The entrance ramp from MD 42 to westbound I-68 forms the fourth leg of the intersection with the other end of MD 742, Maple Street, which receives the exit ramp from westbound I-68. MD 42 heads west up a creek valley to an intersection with Blooming Rose Road, then turns north and crosses Buffalo Run. Shortly after crossing Laurel Run and Glade Run, the state highway passes through the unincorporated community of Asher Glade before the highway reaches its northern terminus at the Pennsylvania state line. The road continues north as SR 2013 toward Markleysburg, where the highway meets PA 281.
History
MD 42 originally connected Friendsville with US 219 north of Accident via Bear Creek Road instead of the current connection near McHenry. The state highway was paved for about east of Friendsville in 1921. The highway was complete to present day US 219 at the hamlet of Kaese Mill north of Accident in 1923. The first section of MD 42 from Friendsville to the Pennsylvania state line was completed in 1928 from the west side of the Youghiogheny River to Blooming Rose Road. The modern Maple Street bridge over the Youghiogheny River was built in 1932. Construction of MD 42 from Blooming Rose Road to the state line began in 1932 and was completed in 1935. MD 42 was transferred from its eastern terminus near Accident to a southern terminus near McHenry, following First Street north to Maple Street within Friendsville, in 1960. The state highway originally followed Hoyes Road east from the crossroads in Hoyes to US 219 north of the present terminus. MD 42 was shifted to its present terminus south of Hoyes around 1972. The state highway was relocated in Friendsville to connect with its interchange with I-68 in 1975; First Street and Maple Street through Friendsville were designated MD 742.
Junction list
Auxiliary route
MD 42A is a connector between MD 42 and MD 828A near Blooming Rose Road west of Friendsville.