Maryland Route 27 (MD 27) is a state highway in the U.S. state of Maryland. Known for most of its length as Ridge Road, the highway runs 39.17 miles (63.04 km) from MD 355 in Germantown north to MD 30 in Manchester. MD 27 follows a ridge that separates several watersheds in northern Montgomery County and Carroll County. The highway connects Germantown and Manchester with Damascus in far northern Montgomery County; Westminster, the county seat of Carroll County; and Mount Airy, which lies at the junction of Carroll, Frederick, Howard, and Montgomery counties and where MD 27 intersects Interstate 70 (I-70) and U.S. Route 40 (US 40).