Partitioned from Nez Perce County and established in 1911,[3] it was named after the explorer Meriwether Lewis.

[5][6][7][8] Early settlement of Idaho by native peoples occurred around 14,000 years ago.

Documented settlement of Idaho's Camas Prairie by the Nez Perce dates back more than 8,000 years with characteristics of the Old Cordilleran Culture appearing in the region.

[9] Characteristics of this culture consist of more sophisticated tools for hunting and the introduction of art forms.

The Nez Perce, like their Shoshoni counterparts of southern Idaho, gained access to escaped Spanish horses from the 16th-century exploration and settlement of New Spain that were traded throughout North America.

The transcontinental Lewis and Clark expedition's Corps of Discovery encountered the Nez Perce tribe in 1805 and camped near Kamiah in the winter of 1806.

They then returned to the main Clearwater River to continue west towards the Pacific Ocean.

Relations with the Nez Perce were amicable until discovery of gold at multiple locations within the reservation's boundaries created tension starting in 1860.

A smaller reservation was negotiated with the Kamiah and Lapwai bands of Nez Perce, with a treaty signed in 1867.

[16] Settlement increased along the route of the Camas Prairie Railroad which reached Reubens in 1906 with operation of the line starting in 1908.

[18] At the 1910 Census, Nez Perce established additional precincts for Chesley, Kamiah, Mason, Mohler, and Winchester.

The county contains the northern portion of the Camas Prairie, an elevated prairie-like region of the middle Columbia basin, south of the Clearwater River.

As of the 2010 United States Census, there were 3,821 people, 1,657 households, and 1,041 families living in the county.