The comune of San Siro incorporates the
frazioni (municipal fractions) of Acquaseria, Camnasco, Carcente, Gallio, La Torre, Lancio Lucena, Marena, Mastena, Maso, Molvedo, Noledo, Pezzo, Rezzonico, Roncate, Santa Maria, San Martino, Soriano and Trecciano. San Siro borders the following municipalities: Cremia, Menaggio,
Plesio; and, on the other side of the lake in the
Province of Lecco:
Bellano,
Dervio and
Perledo. == Etymology ==