Sioux County is a county located in the U.S. state of Iowa. As of the 2020 census, the population was 35,872. Its county seat is Orange City. Its largest city is Sioux Center.

Orange City is a city in, and the county seat of, Sioux County, Iowa, United States. Its population was 6,267 in the 2020 census, an increase from 5,582 in 2000. Named after William of Orange, the community maintains its Dutch settler traditions visibly, with Dutch storefront architecture and an annual Tulip Festival.