Oprah started her broadcasting career in Nashville, Tenn., and Baltimore, Md., before relocating to Chicago in 1984 to host WLS-TV's morning talk show "A.M. Chicago." That show was renamed "The Oprah Winfrey Show" in 1985.
A year later, Winfrey established Harpo and her talk show went into syndication. In 1990, Winfrey opened Harpo Studios in Chicago's West Loop neighborhood.
Tim Bennett, the president of Harpo Productions Inc., says Friday's show will "mark an historic television moment that we will all be talking about for years to come."
You can watch Oprah make the announcement, and her reasons behind it, right here on ABC7 at 3 p.m. PT.
The Associated Press contributed to this report.