Its northern terminus is at Wild Horse Creek Road in Chesterfield; its southern terminus is at Routes W and FF in Jefferson County.

The road continues north, curves around Spirit of St. Louis Airport and connects with Chesterfield Airport Road, providing a "backway" to the Chesterfield area.

The Missouri Department of Transportation commissioned Route 109 sometime between 1937 and 1938 as a state-maintained access road to Babler Memorial State Park from Route C in St. Louis County.

[4][5] A bridge was built over the Meramec River linking Route W from Jefferson County to Route 109's southern terminus at Interstate 44 in 1974,[6][7] but this bridge was later designated to carry Route 109 into Jefferson County, moving its southern terminus to the intersection of Routes W and FF just south of the Meramec River.

In 1999, Route C was fully decommissioned in St. Louis County.