This species has a J-shaped black mark on front of the antenna base. The vertex (top of head between antenna) is reddish orange. One other Oecanthus species has a similar color on top of the head: Davis' Tree Cricket (O. exclamationis) has golden-orange, but it doesn't extend onto the pronotum. Never with dark legs like O. forbesi.
SINA: https://orthsoc.org/sina/584a.htm
Nancy Collins Tree Cricket website: http://www.oecanthinae.com/
The SINA range maps shows this species occurring in most of Iowa, except for parts of the north. But iNaturalist records shows this species occurring well into Minnesota, so it probably occurs statewide.
Usually occurs from the tops of deciduous trees to understory growth and occasionally tall vegetation.