In the Nebraska license plate system, Harlan County is represented by the prefix 51 (it had the 51st-largest number of vehicles registered in the county when the license plate system was established in 1922).

Prior to 1870, the portion of the Republican valley that now includes Harlan County was a prized hunting ground for indigenous peoples, and their efforts to keep intruders away deterred white settlement in the area.

The defeat of the Sioux at the Battle of Summit Springs in 1869 largely eliminated this threat, and several parties were organized to explore the agricultural possibilities of the area.

[3] A party of forty men from eastern Nebraska settled near the site of present-day Orleans in August 1870.

In 1871, a party from the Wyoming Territory, led by Thomas Harlan, settled near present-day Alma,[4] which was named after a settler's daughter.

The terrain consists of gently rolling low hills, with the majority of flat areas being used for center pivot irrigation.