Is aspirin absorbed in the stomach or intestines?

Aspirin is absorbed both in the stomach and the small intestine , for the former the cause lies beyond the fact that the gastric PH (1.5-2.5) is lower than the pka of aspirin (3.5) such that the ionization of aspirin is so much limited and the unionized and subsequently the lipophilicity of aspirin increases so that it's easily absorbed into the gastric mucosal cells.

for the latter , aspirin absorption is due to the large absorptive surface area of the small intestine despite the fact that the intestinal PH is higher than the pka of aspirin , but still the surface area help absorption of the unionized fraction of aspirin.