Theresa Yelverton (née Maria Theresa Longworth; c. 1827–33 – 13 September 1881) was an English woman who became notorious because of her involvement in the Yelverton case, a 19th-century Irish law case, which eventually resulted in a change to the law on mixed religion marriages in Ireland.
Longworth was born in Cheetwood, Manchester, Lancashire, England, the youngest of seven children born to Thomas Longworth, a silk manufacturer. After meeting Major William Charles Yelverton, Viscount Avonmore on a steamer in August 1852, falling in love with him, and pursuing him for several years, she married him secretly on 15 August 1857 at Rostrevor, County Down, Ireland, allowing her to be styled as, and to have earned the title, "Thérèse Yelverton, Viscountess Avonmore". She was a nurse in 1857 in Galata, Russia during the Crimean War.
However, the Viscount remarried within the year, bringing about a series of trials (most notably, Thelwall v. Yelverton, between 21 February 1861 and 4 March 1861) during the course of which he allegedly used his influence with the House of Lords to annul his first marriage. The case brought notoriety and created very mixed feelings. "Theresa was alternately vilified and celebrated, portrayed as a victim who had been 'mercilessly abandoned' and accused of being a lascivious seducer. Sometimes she was depicted as innocent and pure, at others as a ruthless social climber. After six years of trials and appeals, she finally lost her case. In the process, however, she had become a minor celebrity."
Afterwards, she led an itinerant life and supported herself by writing about her travels. Francis Farquhar wrote that she "spent the summer of 1870 in Yosemite, where she attached herself to the Hutchings family and made eyes at John Muir. He escaped to the woods, but not before she had noted enough of his conversation and his ways of life to make him over into Kenmuir, the hero of her novel."
She died in 1881 in Pietermaritzburg, Natal, South Africa.
- History Ireland Magazine (2005) The Yelverton Affair; retrieved 9 December 2005 Archived October 31, 2006, at the Wayback Machine
- Boase, Frederic (1897). Modern English Biography: I-Q. Netherton and Worth. p. 1521. Retrieved 14 July 2017.
- Andrea Wulf, "He's Not That Into You" (review of Schama biography), New York Times, 2 April 2010
- Francis Farquhar, Yosemite, the Big Trees and the High Sierra (University of California Press, 1948), pg. 45
- Martyrs To Circumstance; London: Richard Bentley 1861.
- Saint Augustine, Florida. Sketches of its history, objects of interest, and advantages as a resort for health and recreation; G.P. Putnam & Son: 1869
- Teresina Peregrina; Or, Fifty Thousand Miles of Travel Round the World; two volumes, London: Richard Bentley and Son: 1874
- Teresina In America; two volumes, London: Richard Bentley and Son: 1875
- The Complete Peerage of England, Scotland, Ireland, Great Britain and the United Kingdom, Extant, Extinct or Dormant, new ed., 13 volumes in 14 (1910–1959 by G.E. Cokayne; with Vicary Gibbs, H.A. Doubleday, Geoffrey H. White, Duncan Warrand and Lord Howard de Walden, editors; reprint in 6 volumes, Gloucester, UK: Alan Sutton Publishing, 2000), volume I, pg. 363; also known as The Complete Peerage
- "Wild Romance" a biography of Yelverton by Chloe Schama
- The Yelverton Marriage Scandal
- "Persons and Problems," William Frederic Badè, Life and Letters of John Muir (1924)
- Linnie Marsh Wolfe, Son of the Wilderness, pp. 136–142 (1946) discusses Yelverton and Muir. ISBN 0-299-18634-2
- Zanita: A Tale of the Yo-semite (1872)
- "Introduction" and "Preface" from the 1991 reprint of Zanita, by Margaret Sanborn and Kate Reed, respectively. ISBN 0-89815-410-3
- "Tale of a Tooth", Overland Monthly 11:5 pgs. 434-9 (November 1873) Yelverton's article on Budda's tooth
- Charles Warren Stoddard, In the Footprints of the Padres (San Francisco: A. M. Robertson, 1902) (Library of Congress American Memory) discusses Mrs. Yelverton
- Portrait at National Portrait Gallery