Watertown, South Dakota

===2000 census===
As of the [[census]] of 2000, there were 20,237 people, 8,385 households, and 5,290 families residing in the city. The population density was {{convert|1,328.9|PD/sqmi|PD/km2|sp=us|adj=off}}. There were 9,193 housing units at an average density of {{convert|603.7|/sqmi|/km2|sp=us|adj=off}}. The racial makeup of the city was 96.25% [[White (U.S. Census)|White]], 0.14% [[African American (U.S. Census)|African American]], 1.65% [[Native American (U.S. Census)|Native American]], 0.33% [[Asian (U.S. Census)|Asian]], 0.02% [[Pacific Islander (U.S. Census)|Pacific Islander]], 0.71% from [[Race (United States Census)|other races]], and 0.90% from two or more races. [[Hispanic (U.S. Census)|Hispanic]] or [[Latino (U.S. Census)|Latino]] of any race were 1.28% of the population. 47.1% were of [[germans|German]], 19.8% [[norwegians|Norwegian]] and 5.9% [[irish people|Irish]] ancestry. 96.5% spoke [[english language|English]], 1.7% [[spanish language|Spanish]] and 1.1% [[german language|German]] as their first language.

There were 8,385 households, out of which 31.9% had children under the age of 18 living with them, 50.6% were [[Marriage|married couples]] living together, 8.8% had a female householder with no husband present, and 36.9% were non-families. 30.5% of all households were made up of individuals, and 11.8% had someone living alone who was 65 years of age or older. The average household size was 2.37 and the average family size was 2.98.

In the city, the population was spread out, with 25.9% under the age of 18, 11.3% from 18 to 24, 27.9% from 25 to 44, 19.9% from 45 to 64, and 15.0% who were 65 years of age or older. The median age was 35 years. For every 100 females, there were 96.6 males. For every 100 [[females]] age 18 and over, there were 93.9 [[males]].