Chlorophyll is a green pigment that is present in the cell organelle called chloroplast in plant cells.
It helps in the process of photosynthesis (a biochemical process that converts CO2 and water into Glucose and O2) by trapping the sunlight.
Chloroplast:
These are a type of cell organelle found in plant cells containing chlorophyll.
These organelles are mostly found in the mesophyll cells of leaves and the guard cells of the epidermis. (When dissected, the cross-section of the leaf shows an outermost layer called epidermis followed by a layer of palisade and spongy mesophyll cells.)
Hence, it can be said that chlorophyll pigment is mainly found in the leaves of a plant, to be specific in the chloroplasts found in mesophyll and guard cells of a leaf.