For people with the given name, see Onil. Onil is a town and municipality located in the comarca of L'Alcoià, in the province of Alicante, Valenc…For people with the given name, see Onil. Onil is a town and municipality located in the comarca of L'Alcoià, in the province of Alicante, Valencian Community, Spain. It has an area of 48.41 km² and, according to the 2006 census, a total population of 7466 inhabitants and a population density of 154.22 inhabitants/km². Onil is located next to the mountain called Serra d'Onil in the Serra de Mariola, 36 km from Alicante city.