Katharine Macmillan, Viscountess Macmillan of Ovenden

Katharine Margaret Alice Macmillan, Viscountess Macmillan of Ovenden (née Ormsby-Gore; 4 January 1921 – 22 January 2017), was the daughter of the 4th Baron Harlech, granddaughter of the 4th Marquess of Salisbury, great-granddaughter of the 10th Marquess of Huntly and daughter-in-law of Prime Minister  Harold Macmillan, 1st Earl of Stockton.

On 22 August 1942, she married Conservative politician Maurice Macmillan, making her the daughter-in-law of fellow Conservative politician Harold Macmillan, who would serve as prime minister from 1957 to 1963.

They had five children together:
 * 1) Alexander Daniel Alan Macmillan, 2nd Earl of Stockton (born 1943)
 * 2) Joshua Edward Andrew Macmillan (1945–1965)
 * 3) Adam Julian Robert Macmillan (1948–2016)
 * 4) Rachel Mary Georgia Macmillan (1955–1987)
 * 5) David Maurice Benjamin Macmillan (born 1957)

She was Vice-Chairman of the Conservative Party in 1968 and was created a Dame Commander of the Order of the British Empire (DBE) in 1974. She became Viscountess Macmillan of Ovenden in February 1984 when her father-in-law, former British prime minister Harold Macmillan, accepted a peerage and was created Earl of Stockton. Her husband died the following month, so never inherited the earldom from his father.

She died on 22 January 2017.