The impact of urban migration on ethnic politics is the subject of longstanding debate. “First generation” modernization theories predict that urban migration should reduce ethnic identification and increase trust between groups. “Second generation” modernization perspectives argue the opposite: urban migration may amplify ethnic identification and reduce trust. We test these competing expectations with a three-wave panel survey following more than 8,000 Kenyans over a 15-year period, providing novel evidence on the impact of urban migration. Using individual fixed effects regressions, we show that urban migration leads to reductions in ethnic identification: ethnicity’s importance to the individual diminishes after migrating. Yet urban migration also reduces trust between ethnic groups, and trust in people generally. Urban migrants become “less ethnic” and more suspicious. The results advance the literature on urbanization and politics and have implications for the potential consequences of ongoing urbanization processes around the world.