- Salmon City is a city located in Lemhi County, in the state of Idaho, United States. It is the county seat of Lemhi County and has a population of around 3,112 people as of the 2010 census. The city is situated along the Salmon River and is surrounded by scenic mountain views. It is a popular destination for outdoor activities such as fishing, hunting, hiking, and whitewater rafting. Salmon City has a rich history and is known for its role as a transportation hub during the gold rush in the late 19th century.