Whittier (/ˈhwɪtiər/) is a city in Los Angeles County, California, United States. Part of the Gateway Cities, the 14.7-square-mile (38.0 km²) city had 87,306 residents as of the 2020 United States census. Whittier was incorporated in February 1898 and became a charter city in 1955. The city is named for the Quaker poet John Greenleaf Whittier and is home to Whittier College. The city is surrounded by three unincorporated areas sharing the Whittier name, West Whittier-Los Nietos, South Whittier, and East Whittier, which combined are home to a larger population than Whittier proper.

In the founding days of Whittier, when it was a small, isolated town, Jonathan Bailey and his wife, Rebecca, were among the first residents. They followed the Quaker religious faith and practice and held religious meetings on their porch. Other early settlers, such as Aquila Pickering, also espoused the Quaker faith. As the city grew, the citizens named it after John Greenleaf Whittier, a respected Quaker poet, and deeded a lot to him. Whittier wrote a dedication poem and is honored today with statues and a small exhibit at the Whittier Museum; a statue of him sits in Whittier's Central Park, and another representing his poem "The Barefoot Boy" used to reside by the City Hall and is now in front of the main library. Whittier never set foot there, but wrote the poem "My Name I Give to Thee" about the city. Many of the streets in Uptown Whittier bear the names of Quaker settlers of Whittier or other prominent Quakers, such as Greenleaf Avenue (for Whittier), Bailey Street, Pickering Avenue, Penn Street (for William Penn), Hadley Street and Washington Avenue (both for Washington Hadley), and Painter Avenue (for John Hunt Painter).

The Gabrielino first inhabited the area.

Whittier's roots can be traced to Spanish soldier Manuel Nieto. In 1784, Nieto received a Spanish land grant of 300,000 acres (1,200 km²), Rancho Los Nietos, as a reward for his military service and to encourage settlement in California. The area of Nieto's land grant was reduced in 1790 as the result of a dispute with Mission San Gabriel. Nonetheless, Nieto still had a claim to 167,000 acres (680 km²) stretching from the hills north of Whittier, Fullerton, and Brea, south to the Pacific Ocean, and from what is known today as the Los Angeles River east to the Santa Ana River. Nieto built a rancho for his family near Whittier, purchased cattle and horses for his ranch, and planted cornfields. When he died in 1804, his children inherited his property.

At the time of the 1840s Mexican–American War, much of the land that became Whittier was owned by Pio Pico, a rancher and the last Mexican governor of Alta California. Pio Pico built a hacienda on the San Gabriel River, known today as Pio Pico State Historic Park. After the war, German immigrant Jacob F. Gerkens paid the U.S. government $234 to acquire 160 acres (0.6 km²) of land under the Homestead Act and built the cabin known today as the Jonathan Bailey House. Gerkens later become the Los Angeles Police Department's first chief of police. His land was owned by several others before a group of Quakers purchased it and expanded it to 1,259 acres (5 km²), intending to found a Quaker community. The area soon became known as a thriving citrus ranching region, with "Quaker Brand" fruit shipped all over the United States. Beginning in 1887, walnut trees were planted, and Whittier became the nation's largest walnut grower. In addition to walnuts and citrus, Whittier was also a significant producer of pampas grass.

For many years, the sole means of transport from this area to Los Angeles was by foot or horse and wagon over rough dirt roads, impeding settlement, development, and the export of agriculture. Thus in 1887 "enterprising and aggressive businessmen" contracted with the Southern Pacific Railroad to build the first railroad spur to Whittier, including a depot. The businessmen covered the $43,000 construction cost for the six-mile spur, which branched off from the Southern Pacific mainline at a junction near what is now Studebaker Road between Firestone Boulevard and Imperial Highway. By 1906, 650 carloads of oranges and 250 carloads of lemons were shipped annually by rail. In 1904, the Pacific Electric opened the trolley line known as "Big Red Cars" from Los Angeles to Whittier. In the first two decades, over a million passengers a year rode to and from Los Angeles on the Whittier Line.

During the 1920s and 1930s, Whittier was a conservative sundown town. New housing tracts such as College Hills were developed under restrictive covenants and minorities were restricted to areas outside the city limits such as Jimtown (portions of which were destroyed by the building of the 605 Freeway). Whittier even had a branch of the Silver Shirts. Liquor sales were forbidden in the city; Bailey's Liquor Store was just outside the city limits. Richard Nixon, though born and buried in Yorba Linda, grew up in East Whittier. He attended and played football at Whittier High School (1928–1930) and Whittier College (1930–1934) In the 1930s, Nixon's law office was in the National Bank of Whittier Building in Uptown Whittier. Upon Nixon's return from World War II service, conservative Whittier businessman Herman Perry, Nixon's former landlord at the bank, spearheaded an effort to form a Committee of 100 Republicans in Eastern Los Angeles County to get Nixon elected to Congress in 1946.

After World War II, Whittier grew rapidly. The subdividing of orange groves began, driven by housing shortages in southern California. In 1955, the Civic Center complex was completed, and the City Council met in new chambers for the first time on March 8, 1955. The city continued to grow as it annexed portions of Whittier Boulevard and East Whittier. The 1961 annexation added over 28,000 people to the population, bringing the total to about 67,000. South and West Whittier remained unannexed by the city.