Ontario is a city located in southwestern San Bernardino County, California, United States, 35 miles (56 km) east of downtown Los Angeles. Located in the western part of the Inland Empire region, it lies just east of the Los Angeles county line and is part of the Greater Los Angeles Area. As of the 2010 Census, the city had a population of 163,924, up from 158,007 at the 2000 census, making it the county's fourth most populous city after San Bernardino, Fontana, and Rancho Cucamonga.
The city is home to the LA/Ontario International Airport, which is the 15th busiest airport in the United States by cargo carried. Ontario handles the mass of freight traffic between the ports of Los Angeles and Long Beach and the rest of the country. It is also the home of Ontario Mills and former home of the Ontario Motor Speedway.
It takes its name from the Ontario Model Colony development established in 1882 by the Canadian engineer George Chaffey and his brothers William Chaffey and Charles Chaffey. They named the settlement after their home province of Ontario.