Castelgerundo is a new comune (municipality) in the Province of Lodi in the Italian region Lombardy, located about 55 kilometres (34 mi) southeast of Milan and about 25 kilometres (16 mi) southeast of Lodi.

Casrelgerundo borders the following municipalities: Formigara, Castiglione d'Adda, Maleo, Terranova dei Passerini, Pizzighettone, Cavacurta, Codogno.

[2] The municipality contains also the frazione (subdivision) Bosco Valentino e Mulazzana.

On 22 October 2017 a referendum was held which gave positive results.

The following 28 November the union of the two municipalities was approved by the Regional Council of Lombardy.