The patron saint of Castellanza is Saint Julius, celebrated on 31 January in the Church of San Giulio.
The town also hosts the Palio de la Castellantia, first held on 5 and 6 June 2010: the town is divided into eight districts, including San Bernardo, San Carlo, San Giorgio, San Giovanni, San Giulio, San Simeone, Santa Liberata and Santo Stefano. Castellanza also holds the San Carlo educational archaeology museum and the Pagani Museum Park.