This article argues that variation in public good provision is determined by the salience of demographic and economic regionalism, conceptualized as the presence of multiple large population centers and distinct economic units within a single country’s borders. Two mechanisms—divergent public good preferences and regional self-sufficiency—underpin this relationship. Evidence of these mechanisms as central to low public good provision is found in case studies of Ecuador and Colombia, two countries that score high on standard measures of ethnic diversity and that saw little public good provision during the first century after independence. A region-wide examination of post-independence South America and an investigation of change over time in Venezuela provide further support for the claim that regionalism affects public good provision. A plausible case for this aspect of geography as a cause of low public good provision poses a challenge to the scholarship attributing it to ethnic diversity.