Castellón ; officially in Valencian: Castelló is a province in the northern part of the Valencian Community. It is bordered by the provinces of Valen…Castellón ; officially in Valencian: Castelló is a province in the northern part of the Valencian Community. It is bordered by the provinces of Valencia to the south, Teruel to the west, Tarragona to the north, and by the Mediterranean Sea to the east. The western side of the province is in the mountainous Sistema Ibérico area.