Gut associated lymphoid tissue (GALT) is primarily located in
Lamina propria
Submucosa
Muscularis
Serosa
Apart from its other functions, gastrointestinal tract is a lymphoid organ. The lymphoid tissue within it is collectively known as Gut Associated Lymphoid Tissue, known as GALT.
Gut Associated Lymphoid Tissue (GALT) is primarily located in lamina propria. 
It may be present diffusely or as solitary or aggregated nodules, known as Peyer's patches in the small intestine.