Trenno is a district ("quartiere") of Milan, Italy, part of the Zone 8 administrative division of the city.

It borders on green areas to the north and west (on the Boscoincittà city park) and to the south (on the Parco di Trenno); to the east, it is adjacent to the Gallaratese district.

The district is mostly residential, with low- and medium-income apartment blocks dominating its skyline, although the centre has maintained much of the flavour of a country town (as well as a cascina, "Cascina Campi"); it also has large green areas, the most important of which is the eponymous Parco di Trenno.

The district is quite isolated from Milan, being connected to the centre by a single bus line and a few thoroughfare, some of which were still country roads until the late 1990s.

The settlement of Trenno exists at least since the Middle Ages as a rural borgo close to the Olona river.