The state of Illinois has few natural areas remaining due to anthropogenic changes caused by agriculture, industry, and urbanization. This study investigates the seed plants at the greatest risk of extirpation from Illinois, the state-listed endangered and threatened species, and their occurrence relative to land use. The Illinois Endangered Species Protection Board and the Illinois Natural History Survey chronicle the occurrence and distribution of state-listed endangered and threatened species. We extracted the number of endangered/threatened species per county from these records. We also calculated the proportion of land cover per county for anthropogenic, non-anthropogenic, and protected areas. Using these data, we modeled the distribution of state-listed endangered and threatened seed plants as a function of land cover and human population density. Our study revealed that many endangered plant species are persisting in counties with high levels of human population density. A high degree of agricultural land cover was negatively associated with the presence of endangered/threatened seed plant species. We provide statistical evidence that endangered/threatened species are persistent in highly populated areas, given that there are protected lands with adequate habitat for them to grow. These results underscore the importance of protecting natural habitats. Urban development has preserved some of these habitats by establishing protected lands that allow the continued existence of many species. The role that protected lands play in the conservation of biodiversity is crucial to prevent extirpation of endangered/threatened seed plant species in Illinois.