The causal effects of Catholic schooling on student outcomes have proven challenging to estimate, with several previous studies using the proportion of a geographic unit's population which is Catholic as a potentially exogenous source of variation in the availability of Catholic high schools. We propose a new approach which instead relies on the historical distribution of religious preferences. Specifically, we find that county-level Catholic shares measured at the end of the 19th century are far more strongly associated with Catholic school attendance than are current Catholic shares. Using several strategies, we show that historical Catholic shares are likely to be exogenous to student outcomes conditional on the current distribution of religion. Estimates based on this identification strategy point to smaller Catholic schooling effects than those implied by OLS, in contrast to instrumental variables estimates from previous studies.