Casaleggio Boiro is a comune (municipality) in the Province of Alessandria in the Italian region Piedmont, located about southeast of Turin and about south of Alessandria. As of 31 December 2004, it had a population of 379 and an area of .
Casaleggio Boiro borders the following municipalities: Bosio, Lerma, Montaldeo, Mornese, and Tagliolo Monferrato.