Mission San Gabriel Arcángel was initially founded on September 8, 1771, near settlements of the Tongva people.

It was located in the Whittier Narrows on a bluff overlooking the Rio Hondo, near the modern intersection of San Gabriel Blvd and Lincoln Avenue.

[6] After five years, flooding forced the relocation of the mission to its present site in San Gabriel.

[7] In 1784, Governor Pedro Fages granted to former soldier Manuel Nieto (1734–1804) the largest of the land concessions made in what was then Alta California, a province of New Spain.

Its acreage was slightly reduced later at the insistence of Mission San Gabriel on whose lands it infringed.

At approximately 21,000 acres (8,500 hectares), Santa Gertrudes was itself a sizable rancho and contained the old Nietos homestead, which was a center of social life east of the pueblo of Los Angeles.

Although he was an Irish Democrat, he supported the Republican Lincoln in his efforts to keep the Union intact during the American Civil War.

He pioneered the modern subdivision[12] with land he acquired between the Rio Hondo and the San Gabriel River, in about 1865.

Downey was convinced that oranges would flourish in Southern California, so he imported several varieties, and therefore set in motion what became one of the state's biggest cash crops.

[13] Farmers in the area grew grain, corn, castor beans, and fruit, and by 1935 Downey was characterized as an "orange-grove town".

[14] Vultee became a part of North American Aviation (later North American Rockwell, then Rockwell International which was then bought by the Boeing company) whose facilities were the birthplace of the systems for the Apollo Space Program as well as the Space Shuttle.

For over 70 years, Downey's Rockwell NASA plant produced and tested many of the 20th century's greatest aviation, missile, and space endeavors.

The seventy-year history of airplane and space vehicle manufacturing in Downey came to an end when the Rockwell plant closed in 1999.

Route 19 was a major thoroughfare between Pasadena and the port at Long Beach and Route 42 was along part of the old Spanish El Camino Real trail that connected the Pueblo de Los Angeles to San Diego.

In the 1960s, the town's Downey Records achieved some notoriety with recordings such as The Chantays' surfing instrumental "Pipeline"; nearly two decades later, Downey's local music scene led to the founding of The Blasters and Dark Angel.

Rancho Los Amigos is renowned worldwide for its innovative contributions to the care of spinal cord injuries and post-polio syndrome.

[20] According to the United States Census Bureau the city has a total area of 12.6 square miles (33 km2).

The racial makeup of Downey was 63,255 (56.6%) White, 19,784 (17.7%) Non-Hispanic White,[44] 7,804 (7.0%) Asian (2.2% Korean, 2.2% Filipino, 0.6% Indian, 0.5% Chinese, 0.3% Vietnamese, 0.3% Japanese, 0.2% Thai, 0.1% Cambodian, 0.1% Pakistani), 4,329 (3.9%) African American, 820 (0.7%) Native American, 221 (0.2%) Pacific Islander, 30,797 (27.6%) from other races, and 4,546 (4.1%) from two or more races.

[45] According to the 2010 United States Census, Downey had a median household income of $60,939, with 11.8% of the population living below the federal poverty line.

[52] According to the city's 2021 Comprehensive Annual Financial Report,[53] the top employers in the city are: In the California State Legislature, Downey is in the 30th Senate District, represented by Democrat Bob Archuleta, and in the 64th Assembly District, represented by Democrat Blanca Pacheco.

In 1955, Downey was featured in newspapers worldwide when truck driver George Di Peso lived at 7739 Alderdale Street and had a gopher problem.

According to a July 3, 1955, front-page article in the Los Angeles Times ("Tokyo Awaits Arrival of Downey Hose"), "A message received from Tokyo at the United Press office here read 'Tell Di Peso in Downey the other end of his hose has not turned up here, but we're all still looking.'"

Evidence for the rumor's staying power is in articles in the Los Angeles Times that were published in the 1970s (for example, "Downey Sends L.A. Back to the Bush League," Jack Smith, May 8, 1970).

According to "Zane Grey Also Safe: Tarzan’s Marital Status No Issue as Downey School Ban Is Denied" (Los Angeles Times December 28, 1961), a rumor spread that one of Downey's elementary schools had removed Edgar Rice Burroughs and Zane Grey books from its library because "1—There was no indication that Tarzan and his mate, Jane, were ever married before they took up housekeeping in the treetops," and "2—Grey was known to put such expletives as 'damn!’ and 'hell' in the mouths of his western cowhands."

What happened was that in one elementary school, a parent had put two Zane Grey books "out of site in a desk drawer."

The County of Los Angeles Public Library opened a branch in Downey in September 1915.

In 1958 the Downey City Council voted to establish its own library and withdraw from the county system.

The remodeled city library opened on May 3, 2021, with notable updates including mobile app support for checkouts and a multi-use community space.

[61] In addition, the headquarters of the County of Los Angeles Public Library are located in Downey.

Los Angeles County Metropolitan Transportation Authority (Metro) provides bus services to the city and is served by Lakewood Boulevard station on the C Line.