Psychiatric conditions among women during pregnancy and postpartum can have serious effects on the mother, child, and family including low birth weight, elevated stress, and difficulty parenting. The Military Health System (MHS) provides universal access to care to eligible beneficiaries, which may alleviate some risk factors including low socioeconomic status and lack of private insurance. We sought to evaluate the incidence of psychiatric conditions during pregnancy and one year postpartum between fiscal years (FY) 2019 and 2023. A retrospective cohort study of female TRICARE beneficiaries ages 15-49 who gave birth between FY 2019 and 2023 utilizing claims data from the MHS Data Repository was conducted. Identified deliveries using ICD-10 and MS-DRG codes and psychiatric conditions with ICD-10 codes. Eligibility was restricted to women without a psychiatric diagnosis for two years before delivery and continuously enrolled in TRICARE for a year before and after delivery. Multivariable logistic models were used to determine patient likelihood of developing a psychiatric condition during pregnancy and postpartum. We identified 202,299 deliveries between FY 2019 and 2023, 44,133 (21.8%) where the mother was diagnosed with a new psychiatric condition of which 18,813 (9.3%) were during pregnancy and 25,320 (12.5%) within a year of delivery. Women aged 15-19 (aOR: 1.61, 95% CI: 1.48-1.75) and 20-24 (aOR: 1.22, 95% CI: 1.18-1.26) were more likely to develop a psychiatric condition, while women aged 30-34 (aOR: 0.83, 95% CI: 0.80-0.86), 35-39 (aOR: 0.83, 95% CI: 0.80-0.86), 40-44 (aOR: 0.67, 95% CI: 0.61-0.74) and 45-49 (aOR: 0.65, 95% CI: 0.46-0.91) were less likely when compared to women aged 25-29. Compared to White mothers, Black mothers (aOR: 0.90, 95% CI: 0.87-0.94), Asian/Pacific Islander mothers (aOR: 0.63, 95% CI: 0.59-0.67), Hispanic mothers (aOR: 0.81, 95% CI: 0.78-0.84), and mothers of other race-ethnicity (aOR: 0.85, 95% CI: 0.82-0.88) were less likely to be diagnosed. Active Duty (OR: 1.30, 95% CI: 1.26-1.34) and unmarried women (aOR: 1.20, 95% CI: 1.15-1.25) were more likely to develop psychiatric conditions compared to dependents and married women, respectively. Compared to Senior Officers, Junior (aOR: 1.96, 95% CI: 1.73-2.23) and Senior Enlisted (aOR: 1.45, 95% CI: 1.29-1.64) as well as Warrant Officer and Other rank (aOR: 1.45, 95% CI: 1.23-1.71) had an increased likelihood. Mothers with hypertension (aOR:1.10, 95% CI: 1.06-1.15), diabetes (aOR:1.10, 95% CI: 1.05-1.15), severe maternal morbidity (aOR: 1.47, 95% CI: 1.29-1.67) and preterm delivery (aOR: 1.21, 95% CI: 1.13-1.29) were more likely to be diagnosed with a psychiatric condition. Mothers who delivered in private care (aOR: 0.88, 95% CI: 0.86-0.91) were less likely to develop a psychiatric condition compared to those in direct care. Findings showed that more than one in five deliveries resulted in a psychiatric condition during pregnancy or one year postpartum. Incidence of psychiatric conditions in the MHS were similar to that of the American population. Despite universal access to care, variations in patient likelihood of developing psychiatric conditions across demographic and clinical characteristics were observed. This information can be used to provide resources and tailor treatment for mothers during the perinatal period.