Isabela is the second largest province of the Philippines, and the largest on the island of Luzon in land area. Its capital is the city of Ilagan. Situated within the Cagayan Valley region, it is bordered by the provinces of Cagayan to the north, Kalinga to the northwest, Mountain Province to the central-west, Ifugao and Nueva Vizcaya to the southwest, Quirino to the south, Aurora to the south, and the Philippine Sea to the east.

This primarily agricultural province is the rice and corn granary of Luzon due to its plain and rolling terrain. In 2012, the province was declared as the country's top producer of corn with 1,209,524 metric tons.

Isabela is the 10th richest province in the Philippines in 2011, the only province of Northern Luzon to be included in the list. The province has four trade centers in the cities of Ilagan, Cauayan, Santiago and the municipality of Roxas.

Prior to 1856, the Cagayan Valley was divided into only two provinces: Cagayan and Nueva Vizcaya. The Province of Cagayan at that time consisted of all towns from Tumauini to Aparri in the north. All other towns from Ilagan southward to Aritao comprised the Province of the old Nueva Vizcaya. In order to facilitate the work of the Catholic missionaries in the evangelization of the Cagayan Valley, a royal decree was issued on May 1, 1856 creating the Province of Isabela consisting of the towns of Gamu, Old Angadanan (now Alicia), Bindang (now Roxas) and Camarag (now Echague), Carig (now Santiago City) and Palanan, all detached from the Province of Nueva Vizcaya; while Cabagan and Tumauini were taken from the Province of Cagayan.

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