In the early fifteenth century Palazzo Borromeo was like a "town settlement" consisting of the owner’s nucleus, around which were aggregated smaller courtyards, offices, warehouses, guest apartments and more modest housing for subordinates. This gave prestige to the family from which the palazzo takes its name. A family who had moved to Milan in the late fourteenth century and became one of the leading families of the Milanese aristocracy. In fact, Milanese history recalls important figures who frequented the palazzo such as St.Carlo Borromeo, Cardinal Federico and Giovan Battista who were Francesco Sforza’s advisors.
The palazzo was badly damaged by bombing in World War II and subsequently reconstructed by Ferdinando Reggiori. The building retains the original seventeenth-century style façade in exposed brick which incorporates the beautiful arched portal, consisting of blocks of pink marble from Candoglia and red marble from Verona, adorned with a band depicting grapevines and oak branches under a coat of arms.
A fifteenth century façade still stands in the main courtyard with six large elegant mullioned windows decorated in terracotta with a frieze of a row of interlaced arches below the windowsills. Traces of a fresco can still be seen in the plaster and it is possible to glimpse two of the Borromeo family motifs: a crown and the word "Humiltatis".