Winfrey was picked for the panel Monday. She's one of 12 jurors on the case of 26-year-old Dion Coleman, who's accused in the February 2002 shooting death of another man.
Winfrey occasionally jotted down notes as a 20-year-old witness testified that she saw Coleman shoot 23-year-old Walter Holley.
Reporters and sketch artists filled the front rows of the Cook County Criminal courtroom for Winfrey's jury appearance.
More testimony is planned Tuesday with deliberations expected by Wednesday.