The brain is integral for learning and memory, with no region more important for learning facts and events than the hippocampus. This region develops slowly and is linked to academic success. Understanding functional development will have important consequences on academic achievement and life outcomes for many children. No reliable and valid measure to assess hippocampal function in very young children is currently available. Trace eye-blink conditioning (EBC) is a well-established task with a clear link to hippocampal function and has been extensively used to investigate associative learning in children as young as a few months old. Previous work by our group has shown a relation between trace EBC and hippocampal development. The current study aims to re-examine the relation between trace EBC and hippocampal development by replicating our prior findings in a larger sample and extending our results to consider the subfields of the hippocampus. The hippocampus’ cornu Ammonis (CA) region is made up of four main subfields: CA1, CA2, CA3, and dentate gyrus (DG). In general, these are thought to have different functional attributions with the DG/CA3 being important for fine-grain memories. As part of a larger study, we collected structural MRI and trace EBC from 4–6-year-olds. We preprocessed and analyzed the structural data to extract volumetric information of the hippocampal subfields. We anticipate that DG/CA3 subfield will be associated with greater percentage of conditioned responses and more accurate response latency timed to the unconditioned stimulus. These results will be important because they will offer further proof of the relation between hippocampal structure and performance on trace EBC – thereby providing a task to assess hippocampal function in very young children.