[4][5] Westchester began the 20th century as an agricultural area, growing a wide variety of crops in the dry, farming-friendly climate.

[6][7] In the late 1930s, real estate magnate Fritz Burns and his partner Fred W. Marlow [8] developed a tract of inexpensive prefabricated single-family homes on the site of a former hog farm at the intersection of Manchester and Sepulveda Boulevards.

This community, dubbed "Westchester", grew as the aerospace industry boomed in World War II and afterward.

[9] The 1960s saw the introduction of airliners that could make trans-Pacific flights without refueling, causing a massive increase in air traffic at LAX.

When the North Airfield Complex was constructed the increase in noise from jet takeoffs greatly decreased the desirability of the residential areas adjoining LAX.

The former Manchester Square neighborhood, a 120 acre tract spanning from Aviation to La Cienega and Arbor Vitae to Century, was acquired and demolished piecemeal beginning in 1999.

[15] A densely built-up area consisting of a mix of apartment complexes, duplexes, single family housing and schools, it had a population of over 7,000 in 1998 before the buyout program began.

[17] In 2017 courts authorized the use of eminent domain to acquire the remaining parcels and the last owners all agreed to sell voluntarily shortly afterward.

A major factor has been the influx of technology companies (including Hulu, Google, and Snap, Inc.) in Playa Vista as the Silicon Beach phenomenon in west Los Angeles has spread.

[20] A total of 39,480 people lived in Westchester's 10.81 square miles, according to the 2010 U.S. census, and that figure included the uninhabited acreage of the Los Angeles International Airport—resulting in a density of 3,652 people per square mile, among the lowest population densities in the city of Los Angeles but about average for the county.

[5] In 2010 Non-Hispanic whites made up 61.1% of the population, Blacks 14.2%, Asians 12.0%, Native Hawaiian and other Pacific Islanders 0.3%, and others (including two or more races) at 11.9%.

[5] The 2000 census counted 3,055 military veterans, 9.2% of the population, considered a high percentage for the city of Los Angeles but about average for the county.

[28] The United States Postal Service Westchester Post Office is located at 7381 La Tijera Boulevard.

[29] The United States Postal Service Airport Station is located at 8821 Aviation Boulevard, Los Angeles 90009-9997.

About 51.7% of Westchester's residents had completed a bachelor's degree or higher by 2010, a high figure when compared with the city and the county at large.

The Westchester Senior Citizen Center has a 200-person auditorium, barbecue pits, a 20-person community room, a garden, a kitchen, picnic tables, and a stage.