The best known members of the family were the cardinals and archbishops of Milan, Carlo (1538–1584), who was canonized by Pope Paul V in 1610, and Federico (1564–1631), who founded the Ambrosian Library.

The figure of the Borromean rings, which forms part of the family's coat of arms, is well known in the diverse fields of topology, psychoanalysis, and theology.

[1] The first member of the family to come to prominence was Filippo who, backed by Holy Roman Emperor Charles IV and Gian Galeazzo Visconti (later to become duke of Milan), led the Ghibellines of San Miniato in their 1367 revolt against the Florentine Guelphs.

In 1450 Francesco I Sforza was backed by the family in his struggle to become heir and successor of the Visconti dukes and used the castle as a base for his siege of Milan.

When he became duke, his gratitude for the family's services overwhelmed them with rewards and honours, among which was the title of a count of Peschiera for Vitaliano's son Filippo Borromeo (1419–1464) in 1461.

[5] The "State" was subdivided in ten podesterie: Mergozzo, Omegna, Vogogna, Val Vigezzo, Cannobio, Intra, Laveno, Lesa, Angera and Arona.

The podestà of Arona was the main justice administrator for the Borromeo counts over the area and was independent of both the Novara and Milan jurisdictions, the former controllers.