Capitol is on the Little Missouri River, where it crosses the state line into South Dakota. The post office was established in 1891 with Bernt Anderson as postmaster. Capitol was once known as Capitol Rock. (from Cheney's Names on the Face of Montana, Mountain Press Publishing Company) This name most likely came from today's Capitol Rock National Natural Landmark, located in the Long Pines Unit of Custer National Forest not far from the present day town of Capitol. This massive white limestone uplift is a natural national landmark that resembles the nation's capitol building. Capitol Rock is a remnant of the once continuous blanket of Tertiary deposits that covered much of the Great Plains.The area offers excellent antelope, mule deer, whitetail deer and turkey hunting. The area is also rich in archeology, paleontology, produces some oil, and supports a sizable livestock population. One of the largest populations of Merlins (a small falcon) known in North America occurs in Sioux Ranger District of Custer National Forest.