[6] From 1974 to 1988, the call letters WBMX were held by 102.7 FM, licensed to Oak Park, Illinois (now urban AC station WVAZ).

WCFL-FM, owned by the Chicago Federation of Labor, broadcast from 3 to 9 p.m. as a 400-watt simulcast of WCFL, but the owners surrendered the station's license, as it was not profitable.

[23][24][25] In early August 1984, the station adopted an oldies format as "Magic 104" and its call sign was changed to WJMK.

[32] In early September 1993, John Records Landecker joined WJMK as morning drive DJ, remaining with the station until 2003.

On the same day, veteran oldies station WCBS-FM in New York City made the same switch exactly one hour later at 5 pm.

[48][49] With a format change on WCKG from hot talk to adult contemporary, Steve Dahl and Buzz Kilman moved to WJMK to host mornings on November 5, 2007.

[53][54] On March 10, 2011, CBS Radio announced the station would return to their previous classic hits format as "104.3 K-Hits", setting the time of relaunch for the following Monday, March 14, at 1:04 pm; at 12:30 that afternoon, after playing "Goodbye to You" by Scandal,[55][54][56] the station began stunting with a 34-minute montage of songs and pop culture clips, demarked year by year from 1966 to 1989; at the time promised, "K-Hits" was then launched with "Beginnings" by, fittingly, Chicago.

[57][56] Chicago radio personalities Ed Volkman and Joe "Bohannon" Colborn (Eddie and JoBo) hosted the station's morning show, along with Gary Spears in middays, Bo Reynolds in afternoon drive time and George McFly heard in the evening.

[58][59] Eddie and JoBo were released on December 6, 2012, with the station citing low ratings as the main factor.

[63][64] The rest of the station's final airstaff included Brian Peck in middays and Jeffrey T. Mason in afternoon drive.

[67][68] On November 17, at 10 am, after playing "The Long and Winding Road" by The Beatles and "Changes" by David Bowie, WJMK began stunting with sound effects and clips of a man giving occasional comments, such as "What's going on here?"

"[69] One hour later, WJMK flipped to classic hip-hop, branded as "104.3 Jams", which began with an introduction by legendary rapper, actress, radio DJ, and station voice MC Lyte.

[69][65][70] Entercom applied to move the WBMX call sign to 104.3 from its sister station in Boston to match the new format; the change took effect on December 4, 2017.

[72][73] In addition to WVAZ, WBMX also competes with WPWX and WGCI in the urban radio market.