WMFN (640 AM) is a radio station broadcasting a Black-oriented news format from the Black Information Network. The station is owned by Birach Broadcasting, and under a local marketing agreement with iHeartMedia, specifically its Chicago cluster.

Licensed to Peotone, Illinois, the station currently targets Chicago, specifically the city's South and West Sides, where most of the city's Black population resides. The station's transmitter site is northwest of the intersection of Interstate 57 and (Will/Kankakee) County Line Road south of Peotone.

Though the station in technicality serves the radio market of Will County seat Joliet, along with Morris and Crete, the station's schedule is completely automated with the master feed of BIN and its coverage area de facto serves Chicago and its suburbs, with occasional contributions from personalities from iHeart's WVAZ, WGRB, and WGCI-FM. The station is de facto a full-market satellite station of WVAZ's second HD Radio subchannel, which broadcast BIN before Birach and iHeartMedia entered into the LMA.

The station is a "move in" frequency which originally served West Michigan, and first began broadcasting in Zeeland, Michigan in 1990 under the WBMX call sign, serving Muskegon and Grand Rapids. The station has since been through a number of different formats and call signs, and changed market areas, which is rare for a station.

640 kilohertz is a United States clear-channel frequency, on which KFI in Los Angeles and KYUK in Bethel, Alaska are the dominant Class A stations.

AM 640 was originally a MOR station in 1990 when it signed on as WBMX, using the call sign that had recently been vacated by a popular urban contemporary station in Chicago. The following year, the owners of WROR-FM 98.5 in Boston, Massachusetts, bought the WBMX call letters from 640 in order to debut "Mix 98.5" there; in return, AM 640 received the WROR calls. Its format did not change. In 1993, WROR (AM) was sold and converted to Radio AAHS as WISZ, freeing the WROR calls to be used again in Boston, where they were again placed beginning in 1996.

For a time, the station also played adult standards (Westwood One's AM Only) at night as a continuation of daytimer sister station WMJH 810 AM's format. Since WMJH was known at the time as "Majic 810," WMFN's nighttime standards programming was called "Night Majic."

In 1995, AM 640 became WMFN, taking a sports format branded "West Michigan's Fan". During its sports talk days former NFL linebacker Ray Bentley hosted an afternoon program. In 1999 WMFN adopted a Business News format branded "West Michigan's Financial News". Starting in 2000 WMFN evolved into a News Talk Sports format eventually becoming "Hot Talk 640". In 2005 WMFN's talk format was dropped in favor of an Adult Urban Contemporary format branded "Smooth Vibes AM 640".

From about 2006 until November 2008, the station was leased to Tyrone Bynum, a controversial talk show host and deejay who hosted many of his programs on this station, which went under the name "Smooth Vibes"; during periods when there was no talk programming, Bynum (or his staffers) would play Urban Adult Contemporary music.

In November 2008, due to low advertising revenues, Bynum opted not to renew his lease with Birach; on November 7, 2008, the station began carrying Regional Mexican programming, moved from WMJH. Bynum soon relaunched "Smooth Vibes" as an online-only station free from music licensing fees.

As "La Poderosa," the station became the exclusive Regional Mexican station in West Michigan, as former competitor stations WYGR and WNWZ have switched to other formats. The "Poderosa" format has since moved back to WMJH, which has also launched an FM translator at 93.3. At that time, WMFN became Radio Activa.

In 2014, the FCC allowed the station to be moved to south of Chicago in Peotone. The station aired a Spanish Contemporary format. In summer of 2018, the station aired a Polish language format, Polski FM, simulcasting 92.7 WCPY.

On July 14, 2022, at 1 p.m., WMFN changed their format from Regional Mexican to African-American-oriented news from the Black Information Network.

• WMFN (Corporate) Website
• Michiguide.com - WMFN History
• Facility details for Facility ID 55089 (WMFN) in the FCC Licensing and Management System
• WMFN in Nielsen Audio's AM station database

42°48′59″N 85°57′24″W / 42.81639°N 85.95667°W / 42.81639; -85.95667