Outlaws and Native Americans
The following data is extracted from Days of Yore: Early History of Brown County, Nebraska.
Another class of men sometimes came into this wild, new country. They planned their travels carefully that they might leave no trails for others to follow. They were outlaws who lived by stealing horses from farmers in Iowa and eastern Nebraska. The stolen stock was brought to this lonely country and hid until a safe market could be found for it. The canyons afforded good pasture and safety, Plum creek being well adapted to this purpose. (It was there that the notorious "Doe" Middleton and his band of horse thieves had headquarters, though his home was near Mariaville in what is now called Middleton canyon. The remains of a corral on Hazel Creek, Middleton hill,, said to have been his "lookout" on Plum creek and Doe's lake in Cherry county are, reminders of his residence here in early days.)
All the northwestern portion of this state was at one time known as "unorganized territory" and was given the general name "Sioux County" though there were no county officers. The only government it had was administered from the military posts. The Nebraska state government gradually took this over after 1867 when the territory was admitted to the union. As scattered settlements were made the "unorganized territory" was divided up and counties established. Large companies of settlers came to O'Neill in 1874-'75. Holt County was organized in 1876, and for a few years the land which later became Brown county was attached to Holt for purposes of taxation.
Source: Days of Yore: Early History of Brown County, Nebraska