South Sioux City is located immediately across the Missouri River from Sioux City, Iowa, and is part of the Sioux City metropolitan area.
As of the census of 2000, there were 11,925 people, 4,304 households, and 2,961 families residing in the city.Of the 11,925 people, 48.6% are male and 51.4% are female.The population density was 2,431.6 people per square mile (939.6/km²). There were 4,557 housing units at an average density of 929.2/sq mi (359.1/km²). The racial makeup of the city was 75.88% White, 0.86% African American, 2.36% Native American, 3.19% Asian, 0.09% Pacific Islander, 14.57% from other races, and 3.05% from two or more races. Hispanic or Latino of any race were 24.81% of the population.
There were 4,304 households out of which 38.9% had children under the age of 18 living with them, 49.7% were married couples living together, 13.7% had a female householder with no husband present, and 31.2% were non-families. 25.6% of all households were made up of individuals and 10.3% had someone living alone who was 65 years of age or older. The average household size was 2.72 and the average family size was 3.26.
In the city the population was spread out with 29.8% under the age of 18, 11.1% from 18 to 24, 29.6% from 25 to 44, 19.2% from 45 to 64, and 10.4% who were 65 years of age or older. The median age was 31 years. For every 100 females there were 94.6 males. For every 100 females age 18 and over, there were 92.0 males.
The median income for a household in the city was $36,493, and the median income for a family was $42,712. Males had a median income of $27,259 versus $21,709 for females. The per capita income for the city was $16,165. About 10.1% of families and 11.5% of the population were below the poverty line, including 14.9% of those under age 18 and 8.3% of those age 65 or over.
72.7% of the population held a high school diploma or higher; 12.7% held a bachelor's degree or higher; and 4.8% held a graduate or professional degree. 4.1% of the population were unemployed. Employed residents traveled an average of 15.3 minutes to their jobs.
Several highways serve South Sioux City:
Local bus service to South Sioux City is provided by the Sioux City Transit System.
The nearest commercial airport is Sioux Gateway Airport/Colonel Bud Day Field (SUX) in Sioux City. A smaller general-aviation airport, Martin Field (7K8), is located just west of South Sioux City along U.S. Highway 20.