Between 2000 and 2010, almost all states in the United States experienced population growth. However, as contributions to this growth made by racial/ethnic groups and age cohorts varied from place to place, any discussion of population ‘change’ necessarily refers not only to numerical but also compositional change. This paper presents an analysis of the sources of US population change in the first decade of the new millennium, with an emphasis on changing patterns in population composition in terms of both age and race/ethnicity. Using age and race/ethnicity - specific data from the 2000 and 2010 US decennial censuses - the analysis applies traditional regional analysis tools to identify areas of low or high racial and ethnic concentration and diversity and areas of the country that exemplify ‘typical’ American population composition. In addition, the paper uses shift-share analysis, a descriptive technique most often used to assess employment change across a set of economic sectors, to evaluate state-level population change between 2000 and 2010. The following questions, among others, are answered: Have some states experienced population growth over the past 10 years mainly because the country as a whole has been growing? Or is it more the case that these places had a ‘demographic advantage’ because much of their population is in age cohorts or race/ethnic groups that are growing the fastest? Finally, where does growth appear to be due to region-specific factors? Copyright © 2012 John Wiley & Sons, Ltd.