Note the shape of the wings with a gently angled top margin. The angle is subtle but an important characteristic separating this species from other species. Also note the relatively short legs. Other Katydid species in the Scudderia and Amblycorypha genera have much longer legs, in addition to differently shaped wings.
The similar Microcentrum retinerve (Lesser Anglewing) has not been recorded in Iowa. The shape of the pronotum is different in that species.
SINA: https://sina.orthsoc.org/031a.htm
Capinera, J.L., R.D. Scott, and T.J. Walker. 2004. Field Guide to Grasshoppers, Katydids, and Crickets of the United States. Cornell University Press.
Statewide.
Trees and shrubs. Often attracted to lights at night.