As of the census of 2000, there were 158,007 people, 43,525 households, and 34,689 families residing in the city. The population density was 1,225.5/km² (3,173.9/mi²). There were 45,182 housing units at an average density of 350.4/km² (907.6/mi²). The racial makeup of the city was 47.83% White, 7.51% African American, 1.06% Native American, 3.88% Asian, 0.37% Pacific Islander, 34.05% from other races and 5.30% were from two or more races. 59.88% were Hispanic or Latino of any race.
There were 43,525 households out of which 49.4% had children under the age of 18 living with them, 56.9% were married couples living together, 15.5% had a female householder with no husband present, and 20.3% were non-families. 15.1% of all households were made up of individuals and 4.6% had someone living alone who was 65 years of age or older. The average household size was 3.60 and the average family size was 3.96.
In the city the population was spread out with 34.4% under the age of 18, 11.2% from 18 to 24, 32.4% from 25 to 44, 16.1% from 45 to 64, and 5.9% who were 65 years of age or older. The median age was 28 years. For every 100 females there were 100.6 males. For every 100 females age 18 and over, there were 98.7 males.
The median income for a household in the city was $42,452, and the median income for a family was $44,031. Males had a median income of $31,664 versus $26,069 for females. The per capita income for the city was $14,244. 15.5% of the population and 12.2% of families were below the poverty line. 19.1% of those under the age of 18 and 7.6% of those 65 and older were living below the poverty line.
Ontario has 25 public elementary schools, 6 public middle schools and 5 public high schools under the combined oversight of four school districts. There are also several private schools throughout the city as well as two private military schools. Ontario also has 9 trade schools. Providence Christian College, a 4-year Christian liberal arts college, opened in 2005. The University of La Verne College of Law and Chaffey College Ontario Campus are located in downtown Ontario. Chapman University has a satellite campus near the Ontario Mills mall.
