The Flint Hills region is in Kansas.
The Flint Hills encompasses 13 Kansas counties (Butler, Chase, Chautauqua, Cowley, Elk, Geary, Greenwood, Lyon, Marshall, Morris, Pottawatomie, Riley, Wabaunsee) and smaller areas of 7 peripheral counties (Clay, Dickinson, Jackson, Marion, Ottawa, Saline, Shawnee). Some people are surprised to learn that such a large section of Kansas is so hilly, as much of the rest of the state is relatively flat.
Driving is the best way to get around in this region.
Kansas is a part of Tornado Alley. If you are traveling in this region, it's a good idea to brush up on Tornado safety.