The Great Lakes states face economic, political and social challenges, and population dynamics will influence their future scope and intensity. This report explores population change in six Great Lakes states: Illinois, Indiana, Michigan, Minnesota, Ohio, and Wisconsin. Our analysis relies on census data from 1990 to 2015 and on population projections to 2040 from the Urban Institute’s Mapping Americas Futures model. Over the past 25 years, the population of the Great Lakes states has grown, though more slowly than the US as a whole. The population that is of prime working age has also been growing, and the states are becoming more racially and ethnically diverse. But if current migration patterns persist and population aging proceeds as expected, we project that the region’s population growth will level off. The prime-working age population will decrease (both as an absolute number and as a share of the total population), and the pace of racial and ethnic diversity will increase slightly.