| Ilagan River | |
| Map Size: | 250 px |
| Pushpin Map: | Luzon mainland#Philippines |
| Pushpin Map Caption: | Ilagan River mouth |
| Subdivision Type1: | Country |
| Subdivision Name1: | Philippines |
| Subdivision Type2: | Region |
| Subdivision Name2: | Cagayan Valley |
| Subdivision Type3: | Province |
| Subdivision Name3: | Isabela |
| Length: | 189km (117miles) |
| Discharge1 Avg: | 270m3/s[1] |
| Source1: | Sierra Madre mountains |
| Source1 Location: | Casiguran, Aurora, Central Luzon |
| Source1 Coordinates: | 16.3117°N 121.985°W |
| Mouth: | Cagayan River |
| Mouth Location: | Ilagan, Isabela |
| Mouth Coordinates: | 17.1676°N 121.8904°W |
| Progression: | Ilagan River – Cagayan River |
| Basin Size: | 3132km2 |
The Ilagan River, also known as the Pinacanauan de Ilagan River,[2] is a river in the province of Isabela, Cagayan Valley, Philippines. It is one of the major tributaries of the Cagayan River, the largest river in the Philippines. The Ilagan River originates from the western slopes of the Sierra Madre and drains the eastern central portion of the Cagayan River basin. It has an estimated catchment basin size of [3] and an estimated annual discharge of 9,455 million cubic meters/s. It flows westward and joins the Cagayan River at Ilagan, Isabela.
The major tributaries of Ilagan River are: