Ogallala is a city in and the county seat of Keith County, Nebraska, United States. The population was 4,878 at the 2020 census, up from 4,737 at the 2010 census. In the days of the Nebraska Territory, the city was a stop on the Pony Express and later along the transcontinental railroad. The Ogallala Formation that carries the Ogallala Aquifer was named after the city.