|Origin||Colle Cero, Monti Simbruini|
|Mouth||Liri, Isoletta di Arce|
|Avg. discharge||16 m³/s|
The river is formed by the confluence of two streams of the Monti Simbruini in the Apennines of Abruzzo. It flows towards south-east for a total of 87 km, crossing Ciociaria between the mountain ranges of the Ernici to the north-east, and of the Lepini to the south-west. It flows into the Liri in Isoletta di Arce, in the Lazio.
The Sacco's main tributaries are the Cosa and the Alabro.
In the Frosinone area it is known also the Tolero, from its ancient name Tolerus or Trerus.