MD 109 connects the northwestern Montgomery County communities of Poolesville, Beallsville, Barnesville, and Hyattstown with each other and with Interstate 270 (I-270).

MD 109 begins at the intersection of Elgin Road and Fisher Avenue in the town of Poolesville.

The intersection also serves as the western terminus of MD 107, which heads east along Fisher Avenue through the Poolesville Historic District.

[1][2] The first segment of the highway that became MD 109 was constructed as a macadam road by Montgomery County with state aid by 1910.

[11][12] MD 109's bridge across Little Bennett Creek and its interchange with Washington National Pike (now I-270) were constructed between 1951 and 1953.