This review presents the results obtained and the deductions made from a series of microstructural studies to determine Eutectic Cell Count (ECC), Dendrite Arm Spacing (DAS), and Grain Size (GS) of hypoeutectic gray cast iron which was sand cast using metallic, non metallic, water cooled and sub- zero (Cryogenic) end chills. Analysis of the data on chilled cast iron show that the cooling rate has a marked effect on eutectic cell size, dendrite spacing and grain size. It is observed that, the number of eutectic cells as an index of graphite nucleation and the effect of these on structure and properties, since the eutectic cells are developed on the graphite nuclei during solidification. The review suggest that some of the graphite in the structure of cast iron form more readily as a result of the decomposition of carbides during and after solidification process rather than being an outcome of the direct growth of the graphite form the liquid. It was found that microstructure, DAS, ECC and GS are highly dependent on the location of the casting from where the test samples were taken (chill end) and also on the chilling rate.