Clark County is a county located in the U.S. state of Missouri. As of the 2020 census, its population was 6,634. Its county seat is Kahoka. The county was organized December 16, 1836, and named for William Clark, leader of the Lewis and Clark Expedition and later Governor of Missouri Territory. Clark County is part of the Fort Madison–Keokuk, IA-IL-MO Micropolitan Statistical Area.