Do the authorities in Fahrenheit 451 know about the Book People?
The authorities know about them, but they do not consider them a threat. Faber knows about them, and if he knows about them, then the authorities most certainly do. Faber tells Montag how and where to find the Book people. He says,
"There aren't many of them, and I guess the Government's never considered them a great enough danger to go in and track them down." (pg 132)
Later, when Montag meets the Book people, Granger tells him that there are
"Thousands on the roads, the abandoned railtracks, tonight, bums on the outside, libraries inside." (pg 153)
They are the picture of the model citizen. It is important that they keep a low profile and not cause any disruption of the government because if they are destroyed, the knowledge they have in their heads is gone forever. They are waiting for the war, the one that takes about one minute, so that they can go into what is left and bring their knowledge with them. The government knows that they, as bums and roving individuals, exist, but it does not know of the plan they have for saving books, so they are not worth the government's time. Granger says,
"We're stopped and searched occasionally, but there's nothing on our persons to incriminate us. (pg 152)