Alar del Rey is a municipality in the province of Palencia, within the autonomous community of Castile and León, Spain. It lies in the northern part of the province, in the region of the Tierra de Campos near the border with the province of Burgos.
According to the 2018 census conducted by the Instituto Nacional de Estadística (INE), the municipality had a population of 928 inhabitants. It is one of the smaller municipalities in Palencia, a province characterised by a predominantly rural population spread across numerous small towns and villages.
Alar del Rey is located on the route of the Canal de Castilla, a historic eighteenth- and nineteenth-century canal built for navigation and irrigation across the Castilian plateau. The town is also associated with the nearby source of the Pisuerga river, one of the main tributaries of the Duero.