Lewis County is a county located in the north central region of the U.S. state of Idaho. As of the 2020 census, the population was 3,533, making it the fourth-least populous county in Idaho. The county seat is Nezperce, and Kamiah is the largest city. Partitioned from Nez Perce County and established in 1911, it was named after the explorer Meriwether Lewis. Most of the county is within the Nez Perce Indian Reservation, though Native Americans comprise less than 6% of the county population. Similar to the opening of lands in Oklahoma, the U.S. government opened the reservation for white settlement in November 1895. The proclamation had been signed less than two weeks earlier by President Cleveland.