This is a large area covering 407,000 square kilometres (157,000 sq mi) from northern Illinois through most of Missouri, eastern Kansas, Oklahoma and into Texas.

This area was traditionally a mixture of woodland and tall grass prairie, which as the soil consists of highly fertile mollisols, most of the area has been converted to farmland.

Rainfall varies from 600 to 1040 mm per year and the area is vulnerable to drought and fire.

Remaining blocks of intact habitat are small and include the Emiquon National Wildlife Refuge an important stopover for migrating birds located across the Illinois River from the town of Havana in western Illinois.

Other spots of unspoilt prairie occur in Goose Lake Prairie State Natural Area, Midewin National Tallgrass Prairie and the Kankakee Outwash Plain in Illinois; Indiana Dunes National Lakeshore in northwest Indiana; the Cross Timbers in southern Kansas and central Oklahoma; and the Osage Plains in the south of the ecoregion.