The growth and decline of large village communities is a topic of considerable interest for archaeologists studying the development of complex regional polities. In this article, demographic information is presented for the transitional Mississippian period Washausen mound center located in the American Bottom region of west-central Illinois. Population estimates are calculated based on data for residential architecture collected in 2011 during an extensive geophysical survey and excavations at the site. A magnetometer survey was conducted over 8 ha and produced a relatively complete site map revealing numerous household clusters organized around a central, earthen mound-and-plaza complex. Population estimates and site spatial information for Washausen are compared with similar data for earlier village communities located nearby, as well as other global village sequences, producing a demographic profile demonstrating a pattern of village growth and decline in the area after the onset of sedentism and agricultural intensification. Information from the region and elsewhere suggests that the development of larger communities through time resulted in part through frequent population movements as village segments fissioned and aggregated to form new communities. This research finding has the potential to inform models for the growth of much larger American Bottom centers such as Pulcher and Cahokia.