Sioux City is a city in Woodbury and Plymouth counties in the northwestern part of the U.S. state of Iowa. The population was 82,684 in the 2010 census, which makes it the fourth largest city in Iowa. The bulk of the city is in Woodbury County, of which it is the county seat, though a small 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 168,825 in 2010 and a slight increase to an estimated 169,405 in 2018. The Sioux City–Vermillion, IA–NE–SD Combined Statistical Area had a population of 182,675 as of 2010 but has decreased to an estimated population of 178,448 as of 2018.

Sioux City is at the navigational head, or the most upstream point to which general cargo ships can travel, of the Missouri River, about 95 miles (153 km) north of the Omaha–Council Bluffs metropolitan area. Sioux City and the surrounding areas of northwestern Iowa, northeastern Nebraska and southeastern South Dakota are sometimes referred to as Siouxland, especially by local media and residents.

It is also a part of the Sioux Falls-Sioux City Designated Market Area (DMA), a larger media market region that covers parts of four states and has a population of 1,043,450