Cislago is located on the upper Lombardy plain, close to the Pre-alps. The Cislago area is covered with woodland and is crossed by the Bozzente river, in its new course outside the city. Historically, the town was associated with the Seprio region and the Olona Valley, as it was included in the parish of Olgiate Olona, despite not being on the river itself. Administratively, Cislago belongs to the province of Varese and, along with Gerenzano and Saronno, it forms a kind of "peninsula" between the provinces of Como and Milan.