The formidable parish church was built by the Franciscans in the mid-16th century. A memorial plaque just inside the entrance on your right commemorates Father Stanley Francis Rother, a missionary priest from Oklahoma. Beloved by the local people, Rother was murdered by ultrarightists in the parish rectory next door in 1981; the bedroom where he slept remains open to visitors.
Along the walls of the church are wooden statues of the saints, each of whom has new clothes made by local women every year. At the front stand three colonial altarpieces that were renovated between 1976 and 1981 by brothers Diego Chávez Petzey and Nicolás Chávez Sojuel. These symbolize the three volcanoes around Santiago, which are believed to protect the town. The central one was subtly changed from a traditional European vision of heaven to a more Maya representation of a sacred mountain with two cofradía members climbing toward a sacred cave.