Helenium virginicum (Virginia sneezeweed) is a federally listed threatened herb found at unshaded sites in seasonally inundated ponds in the Shenandoah Valley of Virginia and in the Ozark Highlands of Missouri. In the Ozarks, one population of H. virginicum was discovered in the 1950s, though it was thought to be a hybrid of Helenium flexuosum and Helenium autumnale until genetics work resolved its identity in 2000. Since that time, it was the only known population outside of Virginia. In this study, we systematically identified potential H. virginicum habitat in the Ozarks by using topographic maps and aerial photographs and surveyed these areas for H. virginicum. Our objectives were to locate new populations of the plant and to better define its ecology in Missouri. By the end of the growing season of 2004, we had located 42 new populations of H. virginicum in the lower Missouri Ozarks—more populations than are currently known in the state of Virginia. The results of this study greatly expand the known range of H. virginicum in Missouri and provide important information regarding its ecology.