Castellnovo is a municipality in the comarca of Alto Palancia, in the province of Castellón, within the Valencian Community of eastern Spain. It is one of the smaller settlements of the Alto Palancia district, a largely inland and mountainous area of the province.
The municipality lies in the interior of the province of Castellón, in the northern part of the Valencian Community. Its administrative identity is defined by its status as a municipality within Alto Palancia, one of the comarcas into which the region is organised.
As a Valencian municipality, Castellnovo shares in the administrative and cultural framework of the Valencian Community, where both Spanish and Valencian have official status. The surrounding Alto Palancia comarca is known for its inland, mountainous terrain, in contrast to the coastal plains for which the wider Valencia region is often recognised.