The Duchess of Portland refers to the wife or widow of a Duke of Portland, a former title in the peerage of Great Britain. The title was created in 1716 but became extinct in 1990 upon the death of the ninth Duke.
↑Whitworth, Damian (13 March 2006). "Her amazing grace". The Times. No.68646. p.97. ISSN0140-0460. The story of Margaret, second Duchess of Portland, provides a tantalising glimpse of what might have been... So when Margaret, known as Peggy, married the Second Duke of Portland....
↑"Ivy, Duchess of Portland DBE". The Times. No.61175. 6 March 1982. p.8. ISSN0140-0460. Widow of the seventh Duke of Portland, died on March 3rd. She was 94.