The river is formed by the confluence of Cutler Brook with an unnamed stream, west of the village of Harmony. The river flows in a southeasterly direction to Waterman Lake, then east past the village of Greenville. From there, the river flows in a northerly direction to Stillwater Reservoir where it meets the Woonasquatucket River.
Crossings
Below is a list of all crossings over the Stillwater River. The list starts at the headwaters and goes downstream.