Campoo is a comarca of Cantabria ( Spain) located in the High Ebro, with a surface little bigger than 1,000 km, and including the municipalities of Hermandad de Campoo de Suso, Campoo de Enmedio, Campoo de Yuso, Valdeolea, Valdeprado del Río, Valderredible, Reinosa, Las Rozas de Valdearroyo, Santiurde de Reinosa, Pesquera, and San Miguel de Aguayo. Their inhabitants are called Campurrians (Campurrianos, in Spanish). Its highest elevation is the Cuchillón peak (2,225 m above sea level), and the lowest is Pesquera (560 m), with the capital, Reinosa at 850 m.
Originally, as it is gathered in the Book of Merindades of Castile (from circa 1352), the Merindad of Aguilar de Campoo comprised municipalities of the south of present Cantabria, as well as of northern Province of Palencia and Burgos, with its capital being the Palentine Aguilar de Campoo, ancient capital also of the vast Marquesse of Aguilar de Campoo. Later the capital was moved to Reinosa, which still has this status. The "Palentine Campoo" was left, after the provincial division, with Aguilar as the most important township, and included nowadays into the large comarca of Palentine Mountains.