 Three boundary adjustments were made with Nez Perce and Ada between 1866 and 1867 and Lemhi was created in 1869 from territory east of the junction of the Middle Fork and main Salmon Rivers.In 1873, the southern border was moved north to the divide between the main Salmon River with the Payette River and Middle Fork of Salmon River, bringing the county to its smallest historical land area of 2,901 square miles.The boundary adjustment of 1875 created a county very similar to present Idaho County containing an area of 8,165 square miles.