Only a certain amount of people know like the 3rd, Jiriaya, Kakashi, and some others but whe Naruto was talking with him he said that he didn't want anyone to know because that would of put his life in danger
Question though... Would it really be that unknown? Because, naruto does look a lot like his Dad, and he does still have his moms last name so, wouldn't they know his mom is well his mom.. didn't people know minato was a soon to be father? I always thought it was more to keep people outside the village from knowing. That's what I always thought.. correct me if I'm wrong..