Haplaxius ovatus (Ball) is a little-known cixiid planthopper whose host plants were unknown. During fieldwork in late May, late June—early July, and late August—early September from 2010 to 2013, we collected adults (n = 778) on switchgrass (Panicum virgatum L.; Poaceae: Panicoideae) at 59 sites in nine states: Illinois, Iowa, Kansas, Minnesota, Missouri, Nebraska, Oklahoma, South Dakota, and Wisconsin. New state records are Illinois, Minnesota, Missouri, South Dakota, and Wisconsin. The cixiid was not encountered during less extensive collecting from other prairie grasses: big bluestem, Andropogon gerardii Vitman; little bluestem, Schizachyrium scoparium (Michx.) Nash; Indiangrass, Sorghastrum nutans (L.) Nash; and prairie cordgrass, Spartina pectinata Bosc ex Link. In Nebraska, where switchgrass surveys were most extensive, H. ovatus typically was found in the Tallgrass and Mixedgrass Prairie ecoregions (remnant prairies and roadsides), was uncommon in the Sandhills, and was present along the eastern edge (-102° W longitude) of Shortgrass Prairie. Cixiid nymphs are subterranean, and no attempt was made to detect nymphs of H. ovatus. Male-biased populations and presence of teneral adults (mostly females) in late May, however, suggest a recent emergence from P. virgatum. The few adults taken in late August—early September are assumed to represent those still persisting from the only complete generation (univoltinism). Characters are provided to facilitate the recognition of this switchgrass-associated cixiid. Additional study is needed to verify that H. ovatus overwinters as nymphs, develops on P. virgatum, and is univoltine, as well as determine if it might use related species of Panicum, other panicoid genera, or even non-panicoid grasses as hosts.