Sioux County Courthouse in Harrison, Nebraska; seen from the east. The Classical Revival building was constructed in 1930. It is listed in the National Register of Historic Places. – Ammodramus, Public domain – Wikimedia Commons Sioux County is located in Nebraska. About 1,135 people live here (as of 2020). Between 2010 and 2020, the population declined from 1,311 to 1,135. The area covers about 5,354.0 square kilometers. The region is divided into 3 Subregions. The region was founded in 1877. The name originates from Sioux (Native American and First Nations ethnic group) Sioux County is county in Nebraska, United States. More information at siouxcountyne.gov.