METHODS Most quantitative research on fertility decline in the United States ignores the potential impact of cultural and familial factors. We rely on new complete-count data from the 1880 US census to construct couple-level measures of nativity/ethnicity, religiosity, and kin availability. We include these measures with a comprehensive set of demographic, economic, and contextual variables in Poisson regression models of net marital fertility to assess their relative importance. We construct models with and without area-fixed effects to control for unobserved heterogeneity. CONTRIBUTION All else being equal, we find a strong impact of nativity on recent net marital fertility. Fertility differentials among second-generation couples relative to the native-born white population of native parentage were in most cases less than half of the differential observed among first-generation immigrants, suggesting greater assimilation to nativeborn American childbearing norms. Our measures of parental religiosity and familial propinquity indicate a more modest impact on marital fertility. Couples who chose biblical names for their children had approximately 3% more children than couples relying on secular names, while the presence of a potential mother-in-law in a nearby household was associated with 2% more children. Overall, our results demonstrate the need for more inclusive models of fertility behavior that include cultural and familial covariates.