Now known as “The Voice of Central Illinois” and broadcasting at 1230 AM, WJBC began broadcasting from La Salle, Illinois in May 1925, with 1000 watts. The station was initially music-oriented. When the call letters WJBC were assigned arbitrarily during the AM radio expansion era of the 1920s, the station adopted the mnemonic slogan "Where Jazz Becomes Classic." In September 1934, WJBC began transmitting from new facilities, making it the first radio station in Bloomington-Normal. The transmitter was in Normal and the main studio was at Illinois Wesleyan University in Bloomington; additional studios were at Illinois State Normal School and the Illinois Farm Bureau. At first the station was only on the air a few hours a day with eight daily newscasts, weather twice a day, and the Western Union time announced at the top of each hour.
In 1959, WJBC engineers Ted Bailey and Jack Jenkins demonstrated (and received a patent for) the ATC (Automatic Tape Control) machine at the National Association of Broadcasters convention. This cartridge allowed the “Top 40” concept of fast-paced music, commercials, and jingles to be played with push-button speed and revolutionized radio.