The parishes that today form the municipality of Barro used to belong to the jurisdiction of Peñaflor, in the province of Santiago during the "Antiguo Régimen" (Old Regime). Today's Barro formed part of one of the first constitutional city councils, the one of Trasumia, belonging to the judicial party of Caldas de Reyes. In 1822, when Galicia was divided into four provinces, Caldas de Reyes increased in municipalities; however Ferdinand VII of Spain overruled the changes in 1823 and effectively returned the organization of the Old Regime.