River in Cagayan Valley, Philippines Ilagan River The Ilagan River as it passes through the municipalities of San Mariano (background) and Benito Soliven (foreground). Ilagan River mouth Show map of Luzon Ilagan River (Philippines) Show map of Philippines Native name Pinacauan De Ilagan (Ilocano) Location Country Philippines Region Cagayan Valley Province Isabela Physical characteristics Source Sierra Madre mountains • location Casiguran, Aurora, Central Luzon • coordinates 16°18′42.47″N 121°59′6.98″E﻿ / ﻿16.3117972°N 121.9852722°E﻿ / 16.3117972; 121.9852722 Mouth Cagayan River • location Ilagan, Isabela • coordinates 17°10′7.75″N 121°53′16.85″E﻿ / ﻿17.1688194°N 121.8880139°E﻿ / 17.1688194; 121.8880139Coordinates: 17°10′7.75″N 121°53′16.85″E﻿ / ﻿17.1688194°N 121.8880139°E﻿ / 17.1688194; 121.8880139 Length 189 km (117 mi) Basin size 3,132 km2 (1,209 sq mi) Discharge • average 270 m3/s (9,500 cu ft/s)[1] Basin features Progression Ilagan River – Cagayan River Tributaries • right Abuan River Bintacan River