Isabela comprises an aggregate land area of , representing almost 40 percent of the regional territory. It is the largest province in the island of Luzon and the second largest province in the Philippines by land area. Occupying the central section of the Cagayan Valley region in Luzon, Isabela is bordered by 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, and Aurora to the south. To the east lies the Philippine Sea, making Isabela one of the typhoon-prone provinces in the country.