Firth is a city in Bingham County, Idaho, and the population was 477 at the 2010 census. According to the United States Census Bureau, the city has a total area of 0.54 square miles, all of it land. Firth is located on the eastern side of the Snake River, facing the Blackfoot Mountains. Firth began as a Swedish settlement in 1885. It was named for Lorenzo J. Firth, an English emigrant, who gave land for the railroad section house and water tank; the railroad named the station for him in 1903.