Rising below the col between Rocky Mountain and Balsam Cap, Rondout Creek flows generally southerly down the slopes of Rocky Mountain into a narrow valley, receiving tributary Picket Brook on the left and three unnamed streams from the slopes of Peekamoose Mountain to the right.
It crosses under Peekamoose Road, here also carrying the Long Path hiking trail, again just north of a popular camping area in the small Peekamoose Wild Forest, and then passes the hamlet of Sundown and widens slightly as a floodplain develops alongside.