Peyer patches are large accumulations of malt located only in the

Small intestine

Explanation:

The Peyer patches are usually referred to as those smaller masses of lymphatic tissues and are abundantly present throughout the area of ileum of the small intestine. It plays an important role by protecting the intestine from the various types of bacterial infections, thereby improving the immunity system of the body. They are commonly considered as the aggregated lymphoid nodules.

Thus, these are the large accumulation of malts in the small intestine.