Ralston is a city in Douglas County, Nebraska, United States. The population was 6,494 at the 2020 census. A suburb of Omaha, Ralst…Ralston is a city in Douglas County, Nebraska, United States. The population was 6,494 at the 2020 census. A suburb of Omaha, Ralston is surrounded on three sides by the city of Omaha by 84th, 72nd, and L Streets, and by Sarpy County on the south side.