The county was named for Alexander McKenzie, a territorial political figure who was later disgraced for corruption.

On April 20, 1905, the McKenzie County government was organized, and its previous attachment to Stark was terminated.

The Missouri River flows easterly along the western portion of the county's north boundary line, and the enlargement of the Missouri as it discharges into Lake Sakakawea forms the eastern portion of the county's north and northeastern boundary line.

The county terrain consists of semi-arid rolling hills, carved by river valleys and drainages.

[8] The terrain slopes to the east and north, with its highest point on its south boundary line, at 2,684 ft (818 m) ASL.

The McKenzie County landscape features a wide diversity of physical features, ranging from sugarbeet fields bordering the Missouri River at the northwest corner of the county to rugged badlands near the Little Missouri River in the south, where Theodore Roosevelt National Park and the Little Missouri National Grassland are located.

Between the two rivers is a large area of prairie, ranging from gentle rolling terrain to rocky, rugged pastures.

The southeast corner of the county, bordering on the Little Missouri badlands of neighboring Dunn County, is abundant in wildlife, quaking aspen groves, and bur oak groves, interspersed in places with western red cedar on the north-facing slopes of the badlands.

The southwestern corner counties of North Dakota (Adams, Billings, Bowman, Golden Valley, Grant, Hettinger, Slope, Stark) observe Mountain Time.

The counties of McKenzie, Dunn, and Sioux are split between Mountain and Central Time.