Just ONE planet in the solorsystem has a stargate, and that planet, Earth has just ONE gate, two gates for awhile in history. However, I believe the question was meant to ask how many stargates are in the milky way galaxy, or how many in the entire universe; that answer is much more difficult and would probally be in the tens of thousands! But, as asked, only Earth has a stargate, and only one for the time being.