Lerma is a comune (municipality) in the Province of Alessandria in the Italian region Piedmont, located about 90 km southeast of Turin and about 30 km south of Alessandria.
Lerma borders the following municipalities: Bosio, Casaleggio Boiro, Castelletto d'Orba, Montaldeo, Silvano d'Orba, and Tagliolo Monferrato.