[3] In descending order of land area, it is located in parts of Weston, Converse, Campbell, Niobrara, and Crook counties.

[3] Thunder Basin National Grassland is found along the ecotone, or transition zone, between the Great Plains to the east and the sagebrush steppe to the west, and occurs across a gradient of temperature, precipitation, and elevation.

[4][5] As with grasslands in the Great Plains, the Thunder Basin evolved with disturbance from drought, grazing, fire and burrowing mammals.

[7] Thunder Basin grassland is home to over 100 species of birds; large herbivores such as pronghorn and mule deer; small mammals like black-tailed prairie dogs, white-tailed jackrabbits, cotton tails, kangaroo rats, thirteen lined-ground squirrels, and bats; and predators such as swift fox, badgers, coyote and red fox.

The area includes both sagebrush and grassland plant communities,[8] which interact with a range of ecological disturbances to support diverse wildlife species.