Legnano (Italian pronunciation: [leɲˈɲaːno]; Legnanese: Legnàn or Lignàn) is a town and comune (municipality) in the province of Milan, about 20 kilometres (12 mi) from central Milan. With 60,259, it is the thirteenth-most populous township in Lombardy. Legnano is located in the Alto Milanese and is crossed by the Olona River.

The history of Legnano and its municipal area has been traced back to the 1st millennium BC via archaeological evidence. Already in remote times, in fact, the hills that line the Olona had proved to be habitable places. The town was established in 1261.

Because of the historic victory of the Lombard League over Frederick Barbarossa at Legnano, it is the only town other than Rome named in the Italian national anthem ("[...] Dall'Alpi a Sicilia dovunque è Legnano [...]", en. "From the Alps to Sicily, Legnano is everywhere"). Every year the people of Legnano commemorate the battle with Palio di Legnano. In the institutional sphere, on 29 May, the date of the battle of Legnano, it was chosen as the regional holiday of Lombardy.

Located in the south of the Varese Prealps along the Olona valley [it], the comune of Legnano has an area of 12.72 square kilometers (4.91 sq mi), has an elevation of 192–227 meters (630–745 ft) above sea level, and is seismically classified [it] in Zone 4 (Irrelevant seismology).

The valley soil is mainly composed of sand, gravel, and clay. A thin layer of humus also used to coat the valley, rendering it a moorland useless to agriculture.

Legnano is crossed by the Olona River, which cuts Legnano into two nearly equally sized portions. The Olona has a number of deviations both natural, such as the Olonella [it], located near Visconti Castle, and artificial. The latter of these are the diversionary channels and levees that encase much of the river as it flows through Legnano, especially around the former Cantoni [it] and Dell'Acqua [it] cotton mills.

These were built because the Olona was prone to damaging floods, but consequently made the Olona one of the most polluted rivers in Italy. The pollution of the river is gradually lessening, however, while the last damaging flood occurred on 13 September 1995, and the last in chronological order occurred in July 2014.

For the vast majority of the city's stretch, the waterway is pernilted into levee or stone embankments, which were built to minimize flooding. The Olona, before the construction of embankments and drainage channels, was in fact a river that scourged with frequent floods the areas it crosses.