[8] Ontario handles the mass of freight traffic between the ports of Los Angeles and Long Beach and the rest of the country.

Juan Bautista de Anza is said to have passed through the area on his 1774 expedition, which created a land route between the province of Sonora and San Gabriel.

[18] In 1810, the San Gabriel Franciscans took over the Tongva village of Kaawchama (in today's west Redlands), replacing it with the Guachama rancheria.

)[20] Use of the San Gabriel mission's Rancho Cucamonga was in 1839 granted to Tiburcio Tapia by Alta Californian governor Juan Bautista Alvarado as part of the secularization of California land holdings.

[23] In January 1847, the area became controlled by the United States following the conquest of California as part of the Mexican-American War, and was formalised by the Treaty of Cahuenga.

A road was built between San Bernardino and Los Angeles that year, passing through Rancho Cucamonga.

[21][30] In 1881, the Chaffey brothers, George and William, purchased a parcel of Hellman's Rancho Cucamonga land, and rights to Mount San Antonio water.

They also created the main thoroughfare of Euclid Avenue (California Highway 83), with its distinctive wide lanes and grassy median.

A mule-drawn passenger tramway was used from 1887 to 1895 on the central reservation the Avenue, operated by the Ontario and San Antonio Heights Railroad Company.

Since then it has served the area that is today Ontario, Upland and San Antonio Heights, and to a lesser extent Montclair.

The new "Model Colony" (called so because it offered the perfect balance between agriculture and the urban comforts of schools, churches, and commerce) was originally conceived as a dry town, early deeds containing clauses forbidding the manufacture or sale of alcoholic beverages within the town.

Ontario attracted farmers (primarily growing citrus) and ailing Easterners seeking a drier climate (often to treat tuberculosis).

To impress visitors and potential settlers with the "abundance" of water in Ontario, a fountain was placed at the Southern Pacific railway station.

The stations initially operated as part of The Daily Report, and would go on to change their name, format and ownership many times.

[41] Edwards was infuriated when he learned Durwood had beaten him to a deal with Ontario Mills, and later told him, "I had to teach you a lesson".

The other most common countries of origin outside the United States in Ontario are the Philippines, El Salvador, Guatemala, Vietnam, Korea, China, Honduras, Thailand and Peru.

Shortly thereafter, citrus farmers began taking advantage of Ontario's rocky soil to plant lemon and orange groves.

[61] With California's aerospace industry concentrated in Los Angeles and the Bay Area, the Ontario International Airport was used as a pilot training center.

Major distribution centers are operated by companies such as AutoZone, Cardinal Health, MBM, Genuine Parts/NAPA, and Nordstrom.

[64] According to the city's 2023 Annual Comprehensive Financial Report,[63] the top employers in the city are: The Greater Ontario Convention and Visitors Bureau implemented a tourism marketing district and adopted an aggressive five-year strategic plan focusing on marketing initiatives to bring visitors to the region, build brand and destination awareness while enhancing the local economy.

[67] The Ontario post office contains two oil on canvas murals, The Dream depicting founder Chaffey with surveyors and The Reality which shows a view of the completed Euclid Avenue, painted by WPA muralist Nellie Geraldine Best in 1942.

[69] The scenes, featuring statues by the sculptor Rudolph Vargas, were challenged in 1998 as a violation of church-state separation under the California Constitution by an atheist resident, but the dispute was resolved when private organizations began funding the storage and labor involved in the set-up and maintenance of the scenery in its entirety.

[70] To support the nativity scenes the Ontario Chamber of Commerce started a craft fair called "Christmas on Euclid".

The All-States Picnic, an Independence Day celebration, began in 1939 to recognize the varied origins of the city's residents.

Picnic tables lined the median of Euclid Avenue from Hawthorne to E Street, with signs for each of the country's 48 states.

The Kings relocated the Manchester Monarchs, a franchise they had owned and operated since 2012, and became the Ontario Reign beginning with the 2015–16 AHL season.

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.

The Amtrak Thruway 19 provides twice daily connections from this station to/from Bakersfield to the north, and San Bernardino to the east, with several stops in between.

It connects Ontario with much of the Greater Los Angeles area, Orange County, and the San Fernando Valley.

[79][80] Spanish–American War Congressional Medal of Honor recipient Frank Fulton Ross is buried there, as is George Chaffey, one of the two founders of the city.