Whelan was born in Oakland, California. After attending summer acting camp at age 7, Whelan landed a series of commercials. At age 11, she was cast in the TV show Friends (a little-known 1979 series, not the long-running NBC sitcom spanning the turn of the 21st Century). Later that year, Whelan played the role of Lisa Davis, the sick girl, in Airplane! She is probably best known for her role in the hit television series The Love Boat. In the series she played Vicki Stubing, the daughter of Capt. Stubing (played by Gavin MacLeod). After the show was canceled in 1986, she worked on an album titled Our Time.
After returning to the United States, Whelan moved to New York City and acted in several Off-Broadway productions before leaving the stage to work as an event producer at Madison Square Garden. It was here that she met her second husband whom she would marry over a decade later.
Shortly after leaving MSG, Whelan met her first husband Brad St. John and was married, becoming pregnant soon thereafter. Moving back to her native California in preparation for the birth of her first son Harrison, Whelan soon accepted another acting role on the long-running TV soap opera The Young and the Restless. She then left acting and started working as an investigative producer at LA's KCOP television station where she remained for 4 years before moving back to the east coast to get married again.
She lives in Yardley, Pennsylvania and hosts a Sunday evening radio show on WPHT 1210AM in Philadelphia. The show airs Sunday from 3 pm-4 pm EST. Additionally, Jill teaches acting to children and teens.