I went straight to Wikipedia for this. Their article David (Michelangelo) states:
David is a masterpiece of Renaissance sculpture created between 1501 and 1504, by the Italian artist Michelangelo. It is a 5.17-metre (17.0 ft) marble statue of a standing male nude. The statue represents the Biblical hero David, a favoured subject in the art of Florence. Originally commissioned as one of a series of statues of prophets to be positioned along the roofline of the east end of Florence Cathedral, the statue was instead placed in a public square, outside the Palazzo della Signoria, the seat of civic government in Florence, where it was unveiled on 8 September 1504.
Because of the nature of the hero that it represented, it soon came to symbolize the defense of civil liberties embodied in the Florentine Republic, an independent city-state threatened on all sides by more powerful rival states and by the hegemony of the Medici family. The eyes of David, with a warning glare, were turned towards Rome. The statue was moved to the Accademia Gallery in Florence in 1873, and later replaced at the original location by a replica.
So although you could see a replica at the Florence Cathedral, the real deal is currently at the Accademia Gallery, where it has stood since 1873.