The name was changed to Knox by a statute passed February 21, 1873, which took effect April 1, 1873.

The Missouri River flows eastward along the county's north boundary line.

A smaller drainage, Verdigre Creek, flows northward into the county through the western central part of the county, draining into the Niobrara River shortly upstream of that river's mouth.

[8] As of the 2010 United States Census, there were 8,701 people, 3,647 households, and 2,368 families in the county.

As of the 2000 United States Census,[18] there were 9,374 people, 3,811 households, and 2,595 families in the county.

29.90% of all households were made up of individuals, and 17.40% had someone living alone who was 65 years of age or older.

In no national election since 1936 has the county selected the Democratic Party candidate.