Which is the oldest church in Arizona?
That is open to interpretation. What constitutes a church? Is a church a place where people worship following shared rituals and traditions?
Does a Native American ritual — some slice of Hopi culture, for instance — constitute a church?
Sure, why not? In that case, it's impossible to say what's oldest.
However, if by church you mean the sort of thing that most European cultures have in mind, with a large building, the honors go to the Roman Catholics.
Starting in the 1690s, Catholic missionaries — most notably the Jesuit priest Eusebio Kino — founded a number of missions in what is now southern Arizona.
The beautiful San Xavier del Bac Mission near Tucson is generally recognized as the oldest intact church in the state. The "White Dove of the Desert" was founded in 1692.
St. Paul's Episcopal Church in Tombstone is the state's oldest church that still fulfills its original use. Built in 1882, it featured stained-glass windows from Belgium and original pews from New England.
The first synagogue in the Arizona Territory was the Reform Temple Emanu-El, founded in 1910 in Tucson. Islam has been part of Arizona's religious tapestry for many years, with Muslims meeting in home groups. But I can't say exactly which was the first established mosque in the state.
The first Muslim to enter Arizona history was Estevanico of Azamor, a Moroccan slave who landed in Florida in 1527 and was part of an ill-fated expedition led by Panfilo de Narvaez. Along with two other survivors he crossed the continent, ending up in Spanish Arizona.