Powder River County is a rural, agricultural county of 3297 square miles, located in southeastern Montana. The population density is 0.6 persons per square mile, compared to the Montana average of 6.0 per square mile. The County was created from Custer County on March 17, 1919, and named for the Powder River which runs throught it. The Powder River was named because of the gunpowder-colored sand on its banks. "A mile wide and an inch deep" is a favored description of the river.