Castano Primo borders the following municipalities: Lonate Pozzolo, Vanzaghello, Magnago, Nosate, Buscate, Cameri, Turbigo, Robecchetto con Induno, Cuggiono.

Various periods of struggle and domination by the Visconti followed until, in 1447, Castano came under the control of the House of Sforza who gave it as fiefdom to a family favourite.

In 1848 much of the population emigrated to the nearby Province of Piedmont to escape the repressive rule of the House of Habsburg.

Those sources point to an ancient crest or shield of the town that depicts a red castle from which grows a leafy chestnut tree, still shown today on the stem of the current council.

The suffix "Primo" was added by the then king, Victor Emmanuel II of Italy, by a decree dated 10 December 1863 to distinguish Castano from another town of the same name in the Province of Pavia.