WJDK 103.1 FM began broadcasting August 30,1993 from studio’s in the old Fossen Paint Store at 219 W. Washington Street in downtown Morris. The building was completely renovated to accommodate WJDK and then later WCSJ 1550 AM and even later, WCSJ FM.

The WJDK call letters came from the first initials of the stations co-owners, Jeannine Evenson and Diane Root with the “K” coming from the word “kids.”

In 1997, the 103.1 FM frequency was sold to Big City Radio who combined the frequency with that of two other suburban Chicago frequencies to form a 'trimulcast' under new call letters. At the same time, WCSJ 1550 AM was sold to Larry and Pam Nelson, who acquired a new FM frequency at 95.7. That frequency later became WJDK and both WCSJ and WJDK broadcast from the downtown Morris studios.

When Big City Radio went bankrupt, the Nelson’s purchased back the 103.1 frequency, named it WCSJ FM and began simulcasting with WCSJ AM.