While state incarceration policies have received much attention in research on the causes of mass incarceration in the United States, their roles in shaping population health and health disparities remain largely unknown. Merging data on state incarceration policies to vital statistics birth records from 1984 to 2004, we examine the impacts of two signature state incarceration policies adopted during the “tough on crime” era of the 1990s—three strikes and truth-in-sentencing—on Black and White birth outcomes. Using a difference-in-differences event study research design that models the dynamic impacts of these policies over time, we find that these policies had opposing effects on birth outcomes. Birth weight outcomes—including mean birth weight and low birth weight—for Black infants worsened markedly in the year three strikes policies were adopted. By contrast, birth outcomes for Black and White infants gradually improved after truth-in-sentencing policies were adopted. The discordant findings point to distinct, countervailing mechanisms by which sentencing policies can affect population health. We provide suggestive evidence that three strikes policies adversely impacted Black birth outcomes through affective mechanisms, by inducing highly racialized, stigmatizing, and criminalizing public discourse around the time of policy adoption. Our results indicate that truth-in-sentencing likely impacted birth outcomes via material mechanisms, by gradually reducing community incarceration and crime rates. Altogether, these findings point to the need to further interrogate state criminal legal system policies for their impacts on population health, considering whether, how, and for whom these policies result in health impacts.