The inaccurate statement is: Immune system cells are only located in the cortex.
A lymph node is an organ of the lymphatic system, but since it is the major sites of B and T lymphocytes, and other white blood cells it is also part of the adaptive immune system.
A lymph node consists of an outer cortex and an inner medulla and it is enveloped with fibrous capsule which extends into the lymph node to form trabeculae.
The lymph nodes are filters for the blood found concentrated in the neck, groin, and armpits