The analysis of a new dataset on state prisoners in the 1900 to 1930 censuses reveals that immigrants rapidly assimilated to native incarceration patterns. One feature of these data is that the second generation can be identified, allowing direct analysis of this group and allowing their exclusion from calculations of comparison rates for the “native” population. Although adult new arrivals were less likely than natives to be incarcerated, this likelihood was increasing with their years in the U.S. The foreign born who arrived as children and second generation immigrants had slightly higher rates of incarceration than natives of native parentage, but these differences disappear after controlling for nativity differences in urbanicity and occupational status. Finally, while the incarceration rates of new arrivals differ significantly by source country, patterns of assimilation are very similar.