Salmon is a city in Lemhi County, Idaho. The population was 3,119 at the 2020 census. The city is the county seat of Lemhi County. The Lewi…Salmon is a city in Lemhi County, Idaho. The population was 3,119 at the 2020 census. The city is the county seat of Lemhi County. The Lewis and Clark Expedition crossed the Continental Divide at Lemhi Pass, 30 miles to the southeast of Salmon. They followed the Salmon River through the present site of the city, then ascended the north fork of the river, at the present-day town named after the confluence, to cross into present-day Montana near Lost Trail Pass. The sole female in the party, Sacagawea, was born in the Lemhi Valley near Salmon. The Sacajawea Interpretive, Cultural and Educational Center was opened in Salmon in August 2003.