Maryland Route 109 (MD 109) is a state highway in the U.S. state of Maryland. The highway runs 11.87 miles (19.10 km) from MD 107 in Poolesville north to MD 355 in Hyattstown. MD 109 connects the northwestern Montgomery County communities of Poolesville, Beallsville, Barnesville, and Hyattstown with each other and with Interstate 270 (I-270). The highway was built between Beallsville and Barnesville by 1910. MD 109 was extended to Poolesville in the early 1920s and to Comus in the late 1920s. The route was extended north through its early 1950s interchange with I-270 to Hyattstown in the late 1950s.