The primitive church of Casiglio, probably the chapel of the nearby castle, originally depended on the parish of Carcano. It became an autonomous parish in 1344, thanks to the intervention of Beltramino Parravicini, a member of the noble Erbese family and bishop of Chieti, Como and Bologna. It underwent changes and extensions over the centuries, the last of which is dated 1777.

However, it was completely rebuilt between the years 1842 and 1846. The building is located along the road that leads to the aforementioned castle. It has a simple facade, surmounted by a tympanum. At its side stands a small oratory, used for minor religious functions.

The reconstruction project of the church provided for the subdivision into three naves; the two side chapels were never built and in their place four side chapels were opened.

The presbytery that is inserted into the hall has a rectangular plan.

The most significant work is kept in the first chapel on the right and is the only one that survived the original construction: it is the funeral monument of Bishop Beltramino Parravicini, commissioned on his death (1352) by his brother Zuccone Parravicini.

The monument, in Gothic style, has the figure of the bishop lying at the top (according to some scholars the face is a true portrait of the character) and on the front of the sarcophagus a Crucifixion; it has been attributed to the sculptor Guido da Campione.

On the right wall of the nave, near the presbytery area, there is a seventeenth-century canvas depicting the Baptism of Jesus, attributed to Giovanni Lanfranco and left in deposit to the church by the Pinacoteca di Brera in Milan. On the one opposite, another canvas from the same century represents the Assumption of the Virgin.