An improved understanding of reclassification as a sociodemographic component of urban growth is important for urban planning and sustainable development. However, empirical assessments of the effect of reclassification on urban population dynamics are lacking, especially in countries in the later stage of the urban transition. Using recently available data on spatial reclassification of rural and urban land areas and population, and adopting multiregional demographic methods, we explicitly examine the effects of reclassification, natural growth and rural–urban migration on urban growth in the United States for the intercensal periods of 1990–2000 and 2000–2010. Results suggest that reclassification played a significant role in U.S. urban population change but its magnitude depends on assumptions about the timing of reclassification. The net effect of reclassification on urban change is the largest when reclassification is assumed to occur at the end, and the smallest when assumed to occur at the beginning, of the decennial census periods. While the impact of natural growth on U.S. urban population change is relatively stable, there is significant uncertainty in the effects of reclassification and rural–urban migration. Additionally, international migration is a key source of urban growth in the United States. We find that the places reclassified from rural to urban or from urban to rural experienced the largest changes in population sizes and age composition.