[3] Ilocos is derived from Ylokos, the pre-Hispanic name for the coastal plains stretching from Bangui in the north to Namacpacan in the south.

[4][5] When Spanish explorer Juan de Salcedo arrived in present-day Vigan on June 13, 1572, he observed the area's natural coves and named the region Ylocos and its people Ylocanos.

In 1571, after gaining control over Manila, Spanish conquistadors led by Juan de Salcedo ventured northward with eight armed boats and a small force of 45 men.

Initially administered as part of an encomienda, the Spanish established Christian missions and governmental institutions across Ilocos to convert the native population to Catholicism.

[4] In 1762, the province became part of the independent Free Ilocos state, when Diego Silang declared liberation from Spanish rule, which then momentarily lost control due to the British occupation of Manila.