Reproductive and other hormonal factors have long been associated with an increase in breast cancer rates. It’s unclear whether recent changes in reproductive patterns and use of lower dose exogenous hormones impact the increasing rate of early onset breast cancer in the last two decades. Previous studies also indicated the association between reproductive history and breast cancer risk may differ between white and black women. To better understand hormonal factors related to early onset breast cancer, we conducted a nested case-control study including all breast cancer cases diagnosed among active-duty women in the US military between 2000-2022 (mean diagnosis age of 38). The study includes 711 invasive and 121 DCIS cases with 1711 density sampled controls matched on age and year of diagnosis, race, and year of military enrollment. We evaluated associations with age at last birth and time since last birth with breast cancer among 420 cases and 849 controls who gave birth in the military. Logistic regression models controlling for matching factors estimated the IDR and 95% CI. Any hormonal contraceptive used five or more years increased the rate 42% (95% CI:1.08-1.88) compared to never use. Overall, the breast cancer rate appeared to increase at a later age at last birth. However, this association differed by race; having a last birth at age 35 or older compared to before age 25 increased rates for white women (2.28 (95% CI:1.07-4.99)) but not black women (0.95 (95% CI:0.46-1.92)). Having a birth within ten years of diagnosis was associated with an increased rate (1.22 (95% CI: 0.90-1.65)) after additionally adjusting for number of births. Our findings suggest age and timing of hormonal exposures have an impact on early onset breast cancer rates, though there may be differences by race. Despite the contemporary changes in these hormonal factors, our findings for recent early onset breast cancer parallel those of previous generations.