We do not know much about the history of Caglio. It followed all the events connected with the Parish of Asso, to which it belonged until 1300 and therefore even during the period when the archbishops of Milan were enfeoffed with the Parish (800 1400). Caglio and the Valassina became then fief of the Visconti, who gave it to Facino Cane in 1409. This latter was succeeded by the Dal Verme, important mercenary soldiers. From 1928 to 1947, Caglio was aggregated to the Communes of Rezzago and Sormano, forming the Commune of St. Valeria. This was named after the beautiful, small, Medieval church dedicated to SS. Vitale and Valeria.