<p> Fecal stanol analysis is an emergent geoarchaeological method that provides a proxy of human population change within a watershed. We provide an overview of the method, summarizing previous research and biochemical, geological, and archaeological considerations necessary for the method&rsquo;s success. We apply the method on cores from lake sediments near Cahokia, Illinois, the largest and most well-studied prehistoric mound center in North America. We find fecal stanol data closely track independently established population reconstructions from multiple sources, confirming the utility of the method and demonstrating its viability in warm climates. We compare the Horseshoe Lake fecal stanol record with paleoenvironmental data from this study and others to evaluate the role of flooding, droughts, and environmental degradation in Cahokia&rsquo;s decline. We find Mississippi River flooding and warm season droughts occurred shortly after Cahokia&rsquo;s population maximum, but we find no conclusive evidence of prehistoric environmental degradation in the watershed.</p><p>