We investigate the number and size of local political jurisdictions are determined, by focusing on the tradeoff between the benefits of economies of scale and the costs of a heterogeneous population. We consider heterogeneity in income, race, ethnicity, and religion, and we test the model using American school districts, school attendance areas, municipalities, and special districts. Using cross-sectional and panel analysis, we find very little evidence of tradeoffs between economies of scale

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... d ethnic or religious heterogeneity. However, we find evidence of a tradeoff between economies of scale and income heterogeneity and particularly strong evidence of a tradeoff between economies of scale and racial heterogeneity. To clarify the direction of causality between heterogeneity and jurisdictions, we exploit shocks to racial heterogeneity generated by the two World Wars.