Our objective was to determine if progesterone pretreatment could ameliorate the detrimental effects of lipopolysaccharide (LPS)-induced inflammation on cortical neurogenesis. Timed pregnant mouse dams (n = 8) were given intraperitoneal injections of progesterone (42 mg/kg) or vehicle on embryonic day 17.5. Two hours later, mice were given intraperitoneal LPS (140 μg/kg) or vehicle. Mice were sacrificed 16 hours later on embryonic day 18. Two-color immunofluorescence was performed with primary antibodies T-box transcription factor 2 (Tbr2), ionized calcium binding adapter molecule 1 (Iba1), cleaved caspase 3 (CC3), and 5-bromo-2′-deoxyuridine (BrdU). Cells were counted, and statistical analysis was determined using analysis of variance and Tukey-Kramer method. The Tbr2 intermediate neural progenitor cell density decreased after LPS exposure (P = .0022). Pre-exposure to progesterone statistically increased Tbr2 intermediate neural progenitors compared to LPS treatment alone and was similar to controls (P = .0022). After LPS exposure, microglia displayed an activated phenotype, and cell density was increased (P < .001). Cell death rates were low among study groups but was increased in LPS exposure groups compared to progesterone alone (P = .0015). Lipopolysaccharide-induced systemic inflammation reduces prenatal neurogenesis in mice. Pre-exposure with progesterone is associated with increased neurogenesis. Progesterone may protect the preterm brain from defects of neurogenesis induced by inflammation.