Costa Masnaga is a comune (municipality) in the Province of Lecco in the Italian region Lombardy, located about 35 kilometres (22 mi) northeast of Milan and about 13 kilometres (8 mi) southwest of Lecco.
Costa Masnaga borders the following municipalities: Bulciago, Garbagnate Monastero, Lambrugo, Merone, Molteno, Nibionno, Rogeno.