The pathophysiology of delayed carbon monoxide (CO) encephalopathy remains unclear. In this study, the effects of CO exposure on the dentate gyrus (DG) were investigated in a Wistar rat model by histochemical and molecular methods. Model rats showed significant cognitive impairment in the passive-avoidance test beginning 7 days after CO exposure. Immunohistochemistry showed that compared to the control, the cell number of SRY (sex-determining region Y)-box 2 (SOX2)+/brain lipid binding protein (BLBP)+/glial fibrillary acidic protein (GFAP)+ cells in the DG was significantly less, but the number of SOX2+/GFAP- cells was not, reflecting a decreased number of type 1 and type 2a neural precursor cells. Compared to the control, the numbers of CD11b+ cells and neuron glial antigen 2+ cells were significantly less, but the number of SOX2-/GFAP+ cells was not. Flow cytometry showed that the percent of live microglial cells isolated from the hippocampus in this CO rat model was significantly lower than in controls. Furthermore, mRNA expression of fibroblast growth factor 2 and glial cell-derived neurotrophic factor, which are neurogenic factors, was significantly decreased in that area. We conclude that, in this rat model, there is an association between delayed cognitive impairment with dysregulated adult hippocampal neurogenesis and glial changes in delayed CO encephalopathy.