The station originally held the call sign WLEY and broadcast at 107.1 MHz. WLEY was founded in February 1948, with commercial broadcasts beginning in April. The "LEY" in its call letters stood for Leyden Township, which contains the city of license of Elmwood Park. WLEY was owned by Zeb Zarnecki. The station broadcast in English and Polish. WLEY broadcast the "Polish Barn Dance," hosted by Zeb Zarnecki, along with other programs for the local Polish community. It is not related to today's 107.9 WLEY-FM in Aurora.
The station's studios and transmitter were located on Harlem Ave, in Elmwood Park. It had an ERP of 320 watts at a height above average terrain (HAAT) of 240 feet. In 1949, its ERP was increased to 1,000 watts and its HAAT was increased to 250 feet. In 1955, the station's ERP was increased to 32,000 watts and its frequency was changed to 105.9 MHz, after the previous occupant of that frequency, WFMT, moved to 98.7 MHz. WLEY was taken silent in 1956.
In 1957, the station was sold to Evelyn Chauvin Schoonfield, a school teacher from Detroit, for $22,500, and its call sign was changed to WXFM. In the early 1960s, the FCC investigated several unauthorized transfers of control, which placed renewal of the station's license in jeopardy. However, the FCC allowed Schoonfield to keep the license, and authorized the sale of the station to WXFM Inc., with controlling interest owned by Robert Victor.
In 1970, Triad Radio, a freeform program, began airing on the station.Triad Radio began in 1969, as a three hour weekly program on 105.1 WEAW-FM. The program eventually aired for five hours nightly on WXFM, and continued to air on the station through 1977. Triad Radio published a free monthly magazine that was distributed through retail outlets.
On March 4, 1985, the station's format was changed to album oriented rock (AOR) and its call letters were changed to WCKG. John Records Landecker continued hosting the morning show on WCKG until 1986, when he returned to 890 WLS.
The station began evolving to a hot talk format in July 1996 with the addition of Steve Dahl in the afternoons and Stern returning to mornings, while classic rock continued to air in the remainder of the schedule. In 1998, Jonathon Brandmeier began hosting middays on WCKG, and the station further moved into a hot talk format. During this time, the station was branded "105.9 The PaCKaGe".
On October 25, 2005, the station was rebranded "Free FM." With Stern's departure from terrestrial radio on December 16, 2005, Infinity announced that effective January 3, 2006, WCKG would become the flagship station of Rover's Morning Glory. Following months of poor ratings, Rover's Morning Glory was dropped on August 1, 2006, and was replaced by the New York-based Opie and Anthony Show.
Steve Dahl's son, Matt Dahl, joined WCKG on March 5, 2007, and Garry Meier joined the station on April 2, hosting late mornings. On May 2, 2007, the station's branding was changed from "Free FM" to "Chicago's FM Talk Station." It was later rebranded back to "The Package". By this time, the weekday lineup consisted of Opie & Anthony, Meier, Stan Lawrence & Terry Armour, Steve and Matt Dahl, Glenn Beck, Loveline, and Bill O'Reilly.
October 29, 2007 was the last day of the talk format on WCKG, as hosts and station staff said their goodbyes on-air. Steve Dahl's show continued to air on WCKG, with best-of clips airing for the rest of the day. His show moved to sister station 104.3 WJMK on November 5.
On November 2, CBS Radio gave stories to the media writers at the Chicago Sun-Times and Chicago Tribune that the station would switch to an all-Christmas format that afternoon before the unveiling of its actual new format. However this was a ruse, designed to throw long-time ratings leader 93.9 WLIT-FM off from its plans to start playing all-Christmas music beginning November 8. The trick worked, as WLIT switched to all-Christmas music on November 2nd, while WCKG continued to play the "Best of Dahl" until November 5th. That day, WCKG began stunting by simulcasting several of Chicago's other CBS Radio stations. From 5:30 to 10 a.m., it carried Dahl's first show on WJMK. From 10 a.m. until 2 p.m., it simulcast AM 670WSCR; from 2 to 4 p.m., it simulcast 93.1 WXRT, and from 4 to 5 p.m., it simulcast 780 WBBM.
"Fresh 105.9" logo from 2007 to 2011. The logo remained in use when the format was moved to WCFS's HD2 subchannel from 2011 to 2019.
On February 25, 2008, morning personality Mike LeBaron and midday personality Lisa Greene signed on as the first DJ's on Chicago's "Fresh 105.9." In April 2008, Program Director Mike Peterson named Rick Hall as afternoon host. On October 6, 2009, Roxanne Steele began hosting afternoons on WCFS. Rick Hall moved to mornings on a temporary basis after Mike LeBaron left the station.
In November 2009, Steve Fisher debuted as the new morning host on WCFS. Upon Fisher's arrival, Rick Hall was moved to middays. However, in June 2010, new program director Jim Ryan told reporters that Hall had been released. Evening host Brooke Hunter was moved to middays.
On March 30, 2010, it was announced that Bill Gamble left CBS Radio Chicago, where he was Program Director of WCFS-FM and WUSN.
On the morning of August 1, 2011, WCFS began redirecting listeners to sister stations 96.3 WBBM-FM and 99.5 WUSN. It played an hour and a half of "end"-themed songs, concluding with "End of the Road" by Boyz II Men and the first six seconds of "Don't You (Forget About Me)" by Simple Minds. Then at 8:10 a.m., WCFS replaced the "Fresh" AC format with an FM simulcast of co-owned all-news station 780 WBBM. Until that date, WBBM had been carried on WCFS-HD2, effectively (besides the loss of WCFS's physical staff) making the move merely a swap of the formats for the HD1 and HD2 subchannels.
The format change was seen as a counter to WBBM's new competitor, 101.1 WWWN, which switched to an all-news format on July 31, 2011, one day before WCFS's switch. The "Fresh" AC format was moved to WCFS-HD2 on August 1, rebranding as "The New Sound of Fresh 105.9 HD2."
The move left 93.9 WLIT-FM as the only adult contemporary radio station at the time in Chicago. The switch also gave the NFL'sChicago Bears an FM outlet. WIQI's "FM News" format failed in the market and was replaced by a 90's-centric adult hits format on July 17, 2012.
Though WCFS uses WBBM's on-air branding ("NewsRadio 780 and 105.9 FM, WBBM"), its official call sign remains WCFS, call letters only mentioned once per hour. Arbitron's use of the Portable People Meter for Chicago radio ratings does not need call letter verification to give credit for listening to 105.9 FM. WBBM thus identifies both signals in a rushed form of station identification at :56 past the hour as "WBBM-HD Chicago, WCFS-FM-HD1 Elmwood Park-Chicago."
The two stations have simulcast continuously since August 1, 2011, with one exception. During the 2015 baseball season, WBBM carried Chicago Cubs baseball exclusively over the AM 780 frequency during the 2015 season, while WCFS-FM 105.9 continued to carry the all-news format on its own during Cubs broadcasts. Starting with the 2016 season, the Cubs moved to co-owned 670 WSCR. WBBM and WCFS returned to a full-time simulcast at the end of the 2015 season.
On February 2, 2017, CBS Radio announced it would merge with Entercom. The merger was approved on November 9, 2017, and was consummated on the 17th.
The station's HD2 subchannel debuted in January 2006, and simulcast the all-news format of WBBM AM 780. From 2011 until 2019, the HD2 subchannel had continued to carry an automated version of WCFS's former Hot AC format as "Fresh 105.9", leading to one of the few situations where the station's callsign meaning referred instead to an HD Radio subchannel.