The first inhabitants of what will become Ilocos are the Negritos, who will be pushed out by waves of Austronesians who penetrated the region's narrow coast. These Austronesian settlers will be the ancestors of the Tingguian inhabiting the Cordillera foothills, the Ilocanos in the present areas of Ilocos Norte, Ilocos Sur and northern La Union, the Pangasinan (Pangasinenses) of Pangasinan province and southern La Union, and Sambals in west Pangasinan.

Spaniards arrived in the 16th century, and set up Christian missions throughout the region to convert the natives to Catholicism. Southern (abagatan) Ilocanos and the Pangasinan easily embraced Spanish colonial rule, but not the northern (amianan) Ilocanos who bore deep resentment toward the Spaniards and led many failed revolts against the colonial administrations, most notably the Silang revolts between 1763 and 1764.

During the 1970s, Ilocos region, then also including the Igorot-majority provinces of Abra, Benguet and Mountain Province, was expanded to include Pangasinan, then part of Central Luzon. Followed that is major Ilocano migration, promoted by Ferdinand Marcos (himself an Ilocano), to Abra, Benguet, Mountain Province, and Pangasinan, which was met with resentment from the native Igorot and the Pangasinan, with the former leading an armed insurgency against the Philippine government. Abra, Benguet and Mountain Province would be moved to the new Cordillera region in 1987; the latter two remained majority Igorot with significant Ilocano minorities, while Abra have become majority Ilocano. Pangasinan, meanwhile, remained in Ilocos region, but some native Pangasinan continue to resent the Ilocano migrants. As a result, calling the region simply as "Ilocos" than the longer, official name "Ilocos Region" can be construed as ethnocentric especially in Pangasinan. Ilocano migration & settlement to those areas already happened earlier in 19th century.

Ilocos occupies the narrow plain between the Cordillera Central mountain range and the South China Sea. It also occupies the northern portion of the Central Luzon plain, to the northeast of the Zambales Mountains.

Lingayen Gulf is the most notable body of water in the region and it contains a number of islands, including the Hundred Islands National Park. To the north of the region is Luzon Strait.

The Agno river runs through Pangasinan and empties into Lingayen Gulf. The river flow into a broad delta in the vicinity of Lingayen and Dagupan.

The region's population of 5,000,000 is predominantly Ilocano, with significant Pangasinan, Tagalog and Igorot minorities.

Ilocanos, the largest ethnic group in the region, originate in the two Ilocos provinces, Ilocos Norte and Ilocos Sur, collectively named Ilocandia. They are a predominantly Roman Catholic people, and there are over 8,000,000 Ilocanos spread throughout northern Luzon. Ilocanos also form a significant number of Filipino Americans in California and Hawaii; the majority of them brought to the U.S. as farm workers.

The province of Pangasinan, meanwhile, is home to the Pangasinan people. Also known as the Pangasinense or Pangalatok (the latter they consider derogatory), the Pangasinan form the majority (60%) of Pangasinan's population, and are known for salt production and milkfish (bangus) fisheries. They speak Pangasinan, a language more closely related to the languages of the Ibaloi and Kalanguya Igorot ethnic groups than to Ilocano.

There are also some smaller Igorot populations in Ilocos region, especially the Tingguian and the Isneg at the foothills bordering the Cordillera. The few ethnic Tagalogs are mostly in parts of Pangasinan bordering Tagalog-speaking Nueva Ecija. Sambals or Sambalis inhabit part of western Pangasinan bordering Zambales.

Though slower, buses are the most common way of reaching the region, especially from Manila.

The major carriers serving the region are Victory Liner (and sister bus line Five Star), Dominion Transit, and Partas. Victory and Five Star primarily serves destinations in Pangasinan, while Dominion and Partas serves much of the region through the Manila North Road.

From the south, the main route is the toll Tarlac-Pangasinan-La Union Expressway (TPLEx), whose final segment between Pozorrubio, Pangasinan and Rosario, La Union has been completed in 2021. A free alternative is Route 2, which TPLEx superseded, but remains well-traveled, with many segments widened to 4 to 6 lanes.

The Maharlika Highway (Rte 1/AH26) connects Ilocos Norte with Cagayan Valley, with a scenic section around Pagudpud. Pangasinan-Nueva Ecija Road (Rte 114) runs from Nueva Vizcaya to Pangasinan through a scenic winding route through the southern Caraballo Mountains; it opened in 2023.

Multiple highways connect Ilocos Region with the Cordilleras, from north to south: Rte 204 (from Abra), Rte 205 (from Mountain Province) and Rte 54 (from Baguio)

The only airport with scheduled flights from the Philippines' major airlines is at Laoag (LAO ^IATA), served by Philippine Airlines and Cebu Pacific. The other airports in Lingayen (no IATA), San Fernando (SFE ^IATA) and Vigan (no IATA) only sees general aviation and flight training, except for Vigan airport which is served by charter carrier Platinum Skies.