Hays is home to Fort Hays State University and the Hays Larks, champions of the Jayhawk Collegiate League for most of the 20th century.
As of the census of 2000, there were 20,013 people, 8,230 households, and 4,674 families residing in the city. The population density was 2,635.9 people per square mile (1,018.1/km²). There were 8,772 housing units at an average density of 1,155.3/sq mi (446.2/km²). The racial makeup of the city was 95.43% White, 1.09% Asian, 0.79% African American, 0.24% Native American, 0.02% Pacific Islander, 1.43% from other races, and 0.98% from two or more races. Hispanic or Latino of any race were 2.63% of the population.
Ellis County attracted nearly 1000 Volga German immigrants in the 1870s; for the 2000 census, over 45% of Hays residents identified their ancestry as German.
There were 8,230 households out of which 27.4% had children under the age of 18 living with them, 45.9% were married couples living together, 8.3% had a female householder with no husband present, and 43.2% were non-families. 32.1% of all households were made up of individuals and 10.5% had someone living alone who was 65 years of age or older. The average household size was 2.30 and the average family size was 2.96.
In the city, the population was spread out with 21.5% under the age of 18, 22.2% from 18 to 24, 24.6% from 25 to 44, 18.5% from 45 to 64, and 13.2% who were 65 years of age or older. The median age was 30 years. For every 100 females there were 94.6 males. For every 100 females age 18 and over, there were 91.6 males.
The median income for a household in the city was $31,501, and the median income for a family was $45,552. Males had a median income of $30,022 versus $21,793 for females. The per capita income for the city was $18,565. About 6.7% of families and 14.9% of the population were below the poverty line, including 9.6% of those under age 18 and 9.6% of those age 65 or over.
The Hays Regional Airport provides commercial air service to Kansas City and Denver via Great Lakes Airlines.