As of the census of 2000, there were 17,190 people, 6,851 households, and 4,610 families residing in the city. The population density was 1,794.0 people per square mile (692.8/km²). There were 7,277 housing units at an average density of 759.5/sq mi (293.3/km²). The racial makeup of the city was 86.73% White, 2.30% African American, 0.53% Native American, 0.66% Asian, 0.03% Pacific Islander, 6.84% from other races, and 2.92% from two or more races. Hispanic or Latino of any race were 12.73% of the population.
There were 6,851 households out of which 31.9% had children under the age of 18 living with them, 54.2% were married couples living together, 9.6% had a female householder with no husband present, and 32.7% were non-families. 28.9% of all households were made up of individuals and 12.1% had someone living alone who was 65 years of age or older. The average household size was 2.43 and the average family size was 2.99.
In the city the population had 26.3% under the age of 18, 8.1% from 18 to 24, 28.2% from 25 to 44, 20.8% from 45 to 64, and 16.5% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 93.3 males. For every 100 females age 18 and over, there were 90.1 males.
The median income for a household in the city was $38,236, and the median income for a family was $45,703. Males had a median income of $32,308 versus $21,906 for females. The per capita income for the city was $18,529. About 5.1% of families and 7.9% of the population were below the poverty line, including 9.7% of those under age 18 and 5.6% of those age 65 or over.
Newton is located in Harvey County which is an agricultural and small manufacturing county with 34,361 people. Harvey County Kansas is part of a four county "Metro Area" with about a half million people. The major city in this metro area is Wichita, Kansas, 20 miles (20 minutes) to the South via I-135.
Major highways (I-135, US-50, US-81, K-15), an airport with a 7,002-foot (2,134 m) runway, and the BNSF Railway make Newton a central location for transportation and shipping. Amtrak's Southwest Chief stops in Newton twice each day and provides passenger rail service to either Los Angeles or Chicago.