Tromello is situated in the central Lomellina. The Commune of the province of Pavia is situated on the right bank of the stream Terdoppio, in the Lomellina of the centre.

The origin of the name Tromello is uncertain: it could take origin from the Latin word tres mellum, mell, (in German it means city walls), and it could make reference to walls. Today any hamlet is part of the Commune.