The long coevolutionary history between sunflowers (Helianthus annuus, Asterales: Asteraceae) and arthropods in the northern Great Plains has resulted in a commonly grown oilseed crop that harbors a large diversity of insects. A bioinventory of foliar and subterranean arthropods was performed in 22 sunflower fields over a period of three site years in central and eastern South Dakota. Overall, 467 morphospecies were collected. From foliage, 15 arthropod orders were observed. Those containing the greatest species diversity were Hymenoptera, Coleoptera, Hemiptera, Diptera and Araneae with 80; 53; 53; 40 and 30 morphospecies each, respectively. Subterranean arthropods from 19 orders were collected. The five orders containing the highest number of morphospecies were Coleoptera, Hymenoptera, Hemiptera, Araneae and Diptera containing 77; 17; 14; 11 and nine morphospecies respectively. Although bioinventories can be expensive and time consuming, information gathered from them has many uses, including efforts to assess the implications of pesticide use, wildlife conservation, land use- and climate-change on community structure in sunflowers.