“Thank you all for your kind words and condolences,” she wrote on Instagram. “It gives our family great comfort knowing she lived a good life and is now at peace.”
Vernita Lee, who was 83, died at her home in Milwaukee, Wisconsin, according to a family statement.
She has already been laid to rest at a private funeral, reports say.
Lee, who worked as a housekeeper throughout her life, was born in Mississippi in 1935 and gave birth to Winfrey when she was 18 years old.
She and Winfrey’s father, Vernon Winfrey, never married.
Winfrey was initially raised by her grandmother, before joining her mother and half-siblings, Jeffrey and Patricia (both since deceased), in Milwaukee.
She later moved to live with her father in Tennessee as a teenager.
In 2011, Winfrey revealed on her show that her mother had given up a daughter, also named Patricia, for adoption at birth .