The Santry River rises at an elevation of c. 80m, in the semi-rural areas of Harristown and Dubber in the part of County Dublin now administered by Fingal County Council, near the village of St. Margaret's and Dublin Airport. The lead branch can be found at the end of a small lane in the former Harristown Demesne, now cut off by new road development. The river then flows along to the south of Dublin Airport (from which some tributary streams enter it), near the new Dublin Bus Harristown depot. With the Dubber branch, it passes for most of its upper course out in the open, flowing through Sillogue Public Golf Course and then more of Ballymun; up to this point, the main channel is called Quinn's River.