Drawing on Chicago immigrant communities’ archives, memoirs, and native-language newspapers, this article advances our understanding of Progressive Era environmental politics by delving into cross-class immigrant communities’ views on and activism concerning health. Everyday ethnic Chicagoans—medical and journalistic professionals alongside working-class immigrants—displayed a sophisticated understanding of health. Well versed in medical and scientific germ theories, they embraced a mixture of germ and environmental theories that made them, in effect, “disease ecologists,” revealing a widespread health ecology orientation not limited to the educated white professionals and reformers about whom scholarship has revealed much more. Such perspectives contribute to reinterpretations of earlier scholarly assumptions that germ theory largely displaced environmental analyses. Moreover, ethnic communities’ interpretations of health as ecological underpinned some of their political activism in pursuit of greater environmental parity. Many ethnic activists from across Chicago's class spectrum fought alongside white reformers to rectify environmental health inequities. They sometimes even initiated efforts, displaying an early version of environmental justice activism. At the same time, other cross-class ethnics at least partly blamed individual or ethnic communities’ habits and failures, mirroring to a degree the condescension visible among many Anglo reformers and professionals.