Santiago City, officially City Of Santiago (Ibanag: Siudad nat Santiago; Ilocano: Ciudad ti Santiago; Filipino: Lungsod ng Santiago), is an independent component city located between southwestern part of Isabela and northwestern boundary of Quirino in Northeastern Luzon island of the Philippines. It is the gateway to the vast plains of Cagayan Valley. According to the 2015 census, it has a population of 134,830 people.

Santiago is situated 331 kilometres (206 mi) north of Metro Manila. The city sits on a vast area of predominantly flat and fertile land in the Cagayan Valley, surrounded by the Caraballo Mountains to the south, the Great Sierra Madre to the east and the Cordillera Mountain Range to the west.

Though geographically located within the boundaries of the province of Isabela and part of the province's 4th District, Santiago City is administratively and legally independent from the province as stated in Section 25 of the LGC.

The origin of Santiago City can be drawn from the first native settlement discovered by the early Spanish missionaries at the bank of the old Carig River (now Diadi River) from which its original name, Carig, was derived. The early inhabitants were the Gaddangs and the Ibanags. When the Spanish settled in, the city was named Pueblo of Santiago Apostol de Carig, with Santiago as the Spanish name of Saint James the Apostle. In the early 1950s, the Municipal President Vicente Carreon changed the name to simply Santiago. Santiago remained a municipality for 84 years.

Santiago was originally a part of the province Cagayan (comprising the whole Cagayan Valley region), which was reorganized as a political subdivision in 1583 with Nueva Segovia as its capital. On May 1, 1856, when the Province of Isabela was carved out by a Royal Decree, Santiago was among the towns relinquished to the newly created province. The first five barrios after the Cadastral survey in 1927 were Patul, Batal, Nabbuan, Buenavista and Dubinan.

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