On that date the legislature created another Mercer County, from previously unorganized territory.

The county was named for William Henry Harrison Mercer,[3] (1844–1901), a rancher who settled north of Bismarck in 1869.

[4][5] The northern boundary of Mercer County is delineated by Lake Sakakawea, created in 1956 on the Missouri River.

The county's eastern boundary is delineated by the river as it flows southeastward from the dam that created the lake.

The county terrain consists of rolling hills, largely devoted to agriculture.

[6] The terrain slopes to the north and east; its highest point is near the midpoint of its southern boundary, at 2,451 ft (747 m) ASL.

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

Prior to [9] November 7, 2010, the western portion of Mercer County was in Mountain Time.