Uneven Growth and Unexpected Drivers of Ethnoracial Diversity across Nonmetropolitan and Metropolitan America☆

High levels of ethnoracial diversity are a defining demographic characteristic of U.S. metropolitan areas, but the role of diversity in nonmetropolitan areas is often underappreciated. Here, we use Decennial Census data from 2000 to 2020 to evaluate growing ethnoracial diversity in nonmetropolitan counties and to highlight the uneven geographic distribution of diversity, and changes therein, across nonmetropolitan America. We measure levels of diversity using Simpson's Diversity Index and describe underlying changes in ethnoracial composition. We then produce counterfactual estimates to measure how population change among seven ethnoracial groups has contributed to changes in diversity and compare exposure to diversity across geography and ethnoracial groups. We find that ethnoracial diversity in nonmetropolitan counties has grown by nearly thirty percent in the past twenty years but has remained firmly below that of metropolitan counties. Importantly, nonmetropolitan diversity is increasing due to both growing multiracial and Hispanic populations and the decreasing absolute size of White populations. County‐level exposure to diversity among White populations and populations from minoritized ethnoracial groups has also converged substantially. Overall, growing nonmetropolitan diversity is driven by multiple complex sources and is spatially heterogeneous. Understanding these patterns is important given the centrality of ethnoracial change to the nation's demographic future.