Really important to know that tonsil tissue occurs all around the throat. In adults the main areas are the palatine (faucial) tonsils at the back of the mouth, and the lingual tonsils which are further back, just above the larynx (voice box). This makes the latter invisible unless you have a flexible endoscope, preferably a digital HD one, like mine that took the picture below. This shows a small white tonsil stone in the lingual tonsil, bottom left of the picture.