Although a growing body of research has detected the effects of community‐level religiosity on various health outcomes, very little scholarship has examined the influence of religious ecology on infant mortality rates (IMRs). We conduct ordinary least squares (OLS) regression analyses on postneonatal IMRs (PNIMRs) using county‐level data from the National Center for Health Statistics Linked Birth and Infant Death Data (1990, 2000, and 2006–2010), churches and church membership data, and the Area Health Resource File. We find that while overall rates of postneonatal deaths have decreased over time, the effects of religion on this outcome have become more pronounced. Specifically, we find that counties with greater proportions of mainline Protestant and Catholic adherents exhibit significantly lower PNIMRs. We further find that a greater proportion of conservative Protestants, and especially fundamentalists, increases postneonatal infant mortality. Our findings lend additional support to cultural explanations of U.S. infant mortality.