- Actually it's no longer a secret that Naruto is the host of the nine tails. During Pains invasion he entered the 6 tailed form in the middle of the village so everyone saw that. Also, he is Madara's target in the 4th Shinobi World War, so if the other villages know he is the host, it's just logical that the Konoha 11 do.
It's actually still unknown whether or not they know that he's the Kyubi's Jinchuriki... except for Sakura
Mostly everyone knows by the time Part II begins, Sakura learns of it from Naruto himself in the first Shippuuden arc.
For the last time... the information of the Kyubi and it's host is classified no one that knows of it is supposed to go around blabbing about it... No one in the Konoha11 has officially been told that Naruto is the Kyubi's host except for Sakura, his teammate the rest of them are oblivious to this information***
In episode 9 of Naruto Shippuden Naruto told Temari and Sakura that he was the nine tails Jinchuriki.