Woodbury County is a county located in the U.S. state of Iowa. As of the 2020 census, the population was 105,941, making it the sixth-most populous county in Iowa. The county seat is Sioux City.

Sioux City is a city in Woodbury and Plymouth counties in the northwestern part of the U.S. state of Iowa. The population was 85,797 in the 2020 census, making it the fourth-most populous city in Iowa. The bulk of the city is in Woodbury County, of which it is the county seat, though a small northern portion is in Plymouth County. Sioux City is located at the navigational head of the Missouri River. The city is home to several cultural points of interest including the Sioux City Public Museum, Sioux City Art Center and Sergeant Floyd Monument, which is a National Historic Landmark. The city is also home to Chris Larsen Park, commonly referred to as "the Riverfront", which includes the Anderson Dance Pavilion, Sergeant Floyd Riverboat Museum and Lewis and Clark Interpretive Center. Sioux City is the primary city of the five-county Sioux City, IA–NE–SD Metropolitan Statistical Area (MSA), with a population of 149,940 in the 2020 census. The Sioux City–Vermillion, IA–NE–SD Combined Statistical Area had a population of 175,638 as of 2020.