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.
The LA/Ontario International Airport provides domestic and limited international air travel. Because of the many manufacturing companies and warehouses in the city, the airport also serves as a major hub for freight, especially for FedEx and UPS. This airport is owned by the city of Los Angeles.
Because Ontario is a major hub for passengers and freight, the city is also served by several major freeways. Interstate 10 and the Pomona Freeway (State Route 60) run east-west through the city. Interstate 10 is north of the Ontario airport while the Pomona freeway is south of the airport. Interstate 15 runs in the north-south directions at the eastern side of the city. State Route 83, also known as Euclid Avenue, also runs in the north-south direction at the western side of the city.
Ontario also has a Metrolink station off of Haven Avenue. It connects Ontario with much of the Greater Los Angeles area, Orange County and the San Fernando Valley. Public bus transportation is provided by Omnitrans.