KNX began as a five-watt amateur radio station, 6ADZ, which Fred Christian put on the air on September 10, 1920, broadcasting on a wavelength of 200 meters (1500 kHz). In December 1921, the station moved to 360 meters (833 kHz) and became KGC, sharing time with other stations that broadcast on the same frequency. On May 4, 1922, the station increased power to 50 watts and became KNX. Power was raised to 100 watts in 1923. A year later, Fred Christian sold KNX to Guy Earle, owner of the Los Angeles Evening Express.
During the 1920s KNX, like most stations across the country, changed frequencies several times, landing on 1050 AM as a result of the Federal Radio Commission's reconfigurations of the AM radio band in 1927 and 1928. In 1929, the station's transmitter was upgraded from 500 to 5,000 watts, and in 1932, was raised to 10,000 watts of power. During this time, the station changed owners and was then operated by the Western Broadcast Company. In 1933, the station moved its studios to another part of Hollywood, and was granted permission by the FCC to raise its output to 25,000 watts. The following year, KNX's transmitting power was raised to the nationwide maximum of 50,000 watts, which the station continues presently. It changed to its current 1070 AM channel in 1941.
CBS purchased and began operating KNX as its West Coast flagship station in 1936, ending an eight-year affiliation with KHJ. In 1938, the CBS Columbia Square studios were dedicated for KNX as well as West Coast operations for the entire CBS radio network; that October, the station carried Orson Welles' celebrated version of The War of the Worlds (which KNX has aired every October 30th since). Several legendary performers from the Golden Age of American network radio broadcast from there, including Jack Benny, Bing Crosby, George Burns, Edgar Bergen, and situation comedy star Bob Crane, who was KNX morning man between 1957 and 1965 at the same time he was appearing as a featured supporting player on the ABC television network's The Donna Reed Show.
KNX was a strong competitor in the Los Angeles market while Crane was a morning personality, but began declining in popularity after he left to star in the CBS television series Hogan's Heroes. Following the example of corporate sister station WCBS in New York City, which had enjoyed renewed success with an all-news format, KNX then became an all-news station in the spring of 1968; its first major breaking news coverage was of the assassination of DemocraticPresidential candidateRobert F. Kennedy, in the Ambassador Hotel in Los Angeles, in June of that year.[unreliable source]
In August 2005, KNX moved out of Columbia Square after operating there for 67 years, and began broadcasting from new studios in the Miracle Mile district on Wilshire Boulevard.
In 2009, KNX adopted the slogan "All News, All the Time." It was previously used for 40 years by KFWB, KNX's historic rival in the news radio wars before both became sister stations through the 1995 merger of Westinghouse Electric (KFWB's owner) and CBS. KFWB's format change to news-talk in September 2009 now leaves KNX the only all-news outlet in the Los Angeles area, which is now emphasized in its alternate slogan, "L.A.'s only all-news radio station".
The station's antenna array includes a tall main antenna (193.5 electrical degrees with an efficiency of 400.73 mV/m/kW at 1 km; optimum and much better than average for a Class A station's main antenna, which has a minimum efficiency requirement of 362.10 mV/m/kW at 1 km), and a shorter emergency antenna (145.5 electrical degrees with an efficiency of about 343 mV/m/kW at 1 km; much better than average for a Class A's emergency antenna but inadequate for a Class A station's main antenna), with only one antenna being active at a time. An experiment in the late 1960s which utilized these antennae in a directional setup during the daytime, only, was abandoned and the emergency antenna was later relocated when much of the site was dedicated as a park in Torrance. The residential area to the south of the main antenna was formerly the site of the emergency antenna. The circa-1936 main antenna was replaced after it was destroyed by vandals on September 14, 1965. An unused 365-foot tower was brought in from KFAC-AM and was used while a new 494-foot tower was constructed. These two towers exist today with the 365-foot tower serving as an emergency antenna, having been relocated to the north of the main antenna, within the park. Non-directional Class A stations are expected, and are, with very few exceptions, required to have emergency antennae as these stations serve as regional EAS stations.
KNX features CBS News at the top of each hour. Traffic and weather reports are presented together every ten minutes on the "fives", (:05, :15, :25, :35, :45, :55). Business news from the station is at :10 and :40 past the hour and sports is featured at :20 and :50 past the hour. In addition to stories from their own correspondents, the audio portion of selected reports and weather forecasts from sister television stations KCBS-TV and KCAL-TV are heard on KNX.
The KNX Business Hour, hosted by Frank Mottek, airs at 1 p.m. weekdays and reviews the latest business news immediately following the close of the stock market. On weekends, Food News with Melinda Lee airs at 10 a.m. - 12 noon.  The CBS News Weekend Roundup and 60 Minutes also air on Saturday and Sunday, respectively.