Omaha is the largest city in the U.S. state of Nebraska and the county seat of Douglas County. Omaha is in the Midwestern United States on the Missouri River, about 10 miles north of the mouth of the Platte River. The nation's 39th-largest city, Omaha's 2020 census population was 486,051. It is the second-largest city in the Great Plains states, the second-largest city along the Missouri River, and the seventh-largest city in the Midwest.