The first traces of human presence in the area date to c. 60,000 years ago, when Neandertal hunters settled here. A site with rock paintings, dating to c. 10,000/6,500 years ago, has been discovered near la Sarga. From around the mid-3rd millennium BC people started to move from the caves to the plain where cereals were grown, while mountain fortifications were erected (Mola Alta de Serelles, Mas del Corral, Mas de Menente, El Puig).
After the Roman conquest of the Iberians, several rural villas were built in the area, as well as a necropolis. The town was established in 1256 by James I of Aragon, with the construction of a castle on a strategic position over the Serpis river, to secure the southern frontier of the Kingdom of Valencia during the Reconquista.
In 1291 the town was donated by King James II of Aragon to the Sicilian admiral Roger of Lauria; it will not return a royal possession until 1430.
During the War of Spanish Succession, Alcoi sided for the cause of archduke Charles, and was therefore besieged and stripped of numerous privileges, which started a period of decline.
In 1873 the workers of Alcoy revolted in the Petroleum Revolution.