Above Langnau am Albis, some 13 km (8.1 mi) from the confluence with the Limmat, there are no major settlements alongside the river, and only a few small villages.

Whilst the town of Einsiedeln is situated close to the Sihlsee, it is actually in the valley of a tributary river, the Alp.

[3] The name may be of Old European or Celtic origin: *Sîla ("quiet watercourse", from a root *sîl = "to trickle, wet") > Romance Sila with the addition of the Old High German element aha "flowing water".

[4] The river rises to the north-eastern side of the Druesberg mountain, in the municipality of Unteriberg of the canton of Schwyz, and flows north to the village of Studen.

Some 2 km (1.2 mi) downstream of Studen, the river enters the artificial Sihlsee reservoir at its southern end.

North of Sihlbrugg, the river flows through a lightly populated and heavily wooded valley, accompanied by a main road and railway line.

At this point, Lake Zürich lies only 2 km (1.2 mi) to the east, but is separated from the river by the Zimmerberg mountain.