|Main source||Colle Cero, Monti Simbruini|
|River mouth||Liri, Isoletta di Arce|
|Length||87 km (54 mi)|
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 kilometres (54 mi), 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.
The Sacco river valley is a vast territory between the provinces of Rome and Frosinone in the central-southern Italy. The intensive exploitation that for decades affected of this valley due to no-scruple companies and crooked public administration offices, produced an unprecedented environmental and social disaster.