[1] Its eastern border is the Missouri River and its county seat is Fort Yates.

It was named for the Native American Lakota, whose historic territory included this area.

Porcupine Creek flows southeastward into the Missouri River, draining the northeastern part of the county.

The county terrain consists of low rolling hills etched with gullies and drainages; the area is mostly devoted to agriculture.

[4] The terrain slopes to the east and south; its highest point is on the west line, near the southwestern corner of the county, at 2,602 ft (793 m) ASL.

[6] The southwest corner counties of North Dakota (Adams, Billings, Bowman, Golden Valley, Grant, Hettinger, Slope, and Stark) observe Mountain Time.

The counties of McKenzie, Dunn, and Sioux are split, observing Mountain Time in their western portions.