The patron of Cengio is Saint Catherine of Siena, celebrated on 29 April. The town is organised into several districts, each with its own church: in the district of Bormida stands the parish church of San Giuseppe, erected in 1955 and restored in 2010, which houses a mosaic behind the altar centred on the saint's statue and two side chapels off the presbytery, the baptistery and one dedicated to the Blessed Sacrament; while it was being completed, an 18th-century church served as the parish church.
In the district of Genepro instead stands the parish church of Santi Barbara e Giovanni Battista, erected in the neo-Romanesque style in the early 20th century from a civil-industrial structure that belonged to the nearby SIPE plant. The municipal territory also contains the sanctuary of the Nativity of the Virgin Mary, as well as the Nature Reserve of the Sources of the Belbo.
