Nez Perce County is a county located in the U.S. state of Idaho. As of the 2020 census, the population was 42,090. The county seat is Lewiston. The county is named after the Native American Nez Perce tribe. Nez Perce County is part of the Lewiston, Idaho–WA Metropolitan Statistical Area.

Lewiston is a city and the county seat of Nez Perce County, Idaho, United States, in the state's north central region. It is the third-largest city in the northern Idaho region, behind Post Falls and Coeur d'Alene, and the twelfth-largest in the state. Lewiston is the principal city of the Lewiston, ID-WA Metropolitan Statistical Area, which includes all of Nez Perce County and Asotin County, Washington. As of the 2020 census, the population of Lewiston was 34,203, up from 31,894 in 2010.