This article assembles new data and methods for studying wealth inequality trends in industrializing America. Inequality grew sharply between 1820 and 1850, leveled off, and increased steadily between 1870 and 1900. Inequality grew due to compositional changes in the population, but also grew within occupations, age groups, and the native-born population. Proposed labor-market explanations are inconsistent with the fact that wealth inequality between occupational groups was declining. Wealth accumulation patterns are also inconsistent with the hypothesis of child default on responsibilities for old-age care. We propose research on a new explanation based on luck, rents, and entrepreneurship.