Microglia, the brain's resident immune cells, play an important role in the maintenance of normal brain function, and in the brain’s response to disease and injury. The hippocampus is an area of focus for microglial study due to its central role in numerous behavioral and cognitive functions. Interestingly, microglia and related cells in the hippocampus and throughout the brain are distinct in male vs. female rodents, even in early life. However, sex differences in hippocampal microglia have not been examined in the P10 mouse hippocampus. In addition, key subregions of the hippocampus — CA3 and the dentate gyrus (DG) hilus — have not yet been assessed for sex differences in microglia. To address these knowledge gaps, the objectives of our study were to quantify microglial (Iba1+) cell densities and classify microglial (Iba1+) cell morphologies in four hippocampal subregions (DG molecular layer, DG hilus, CA1, and CA3) in P10 male and female C57BL/6J mice. The results from this study provide us with a baseline that will be crucial for future experiments in which we will evaluate sex differences in microglial cell density and morphology in a mouse model of perinatal hypoxic-ischemic brain injury, to model the human condition of hypoxic-ischemic encephalopathy (HIE). Elucidating the role of microglia in the sex-dependent response to perinatal hypoxia-ischemia could provide us with critical knowledge for the development of novel therapies for children with HIE.