Cheyenne County is a county in the U.S. state of Nebraska. As of the 2020 United States Census, the population was 9,468. Its county seat is Sidney. The county was formed in 1871 and named for the Cheyenne Native American tribe.

Sidney is a city in and the county seat of Cheyenne County, Nebraska, United States. The city is nine miles (14 km) north of the Colorado state line. The population was 6,410 at the 2020 census.