The Vatican citizenry consists almost entirely of two groups: clergy working as officials of the Vatican as a state or of the Catholic Church; and the Swiss Guard.
Most of the 3,000 lay workers who comprise the majority of the Vatican work force reside outside the Vatican and are citizens of Italy, while a few are citizens of other nations.
As a result, all of the City's actual citizens are Catholic.
Catholicism is the state religion and all the places of worship inside Vatican City are Catholic.