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Later life and death

In his later years, Twain lived at 14 West 10th Street in Manhattan. He passed through a period of deep depression which began in 1896 when his daughter Susy died of meningitis. Olivia's death in 1904 and Jean's on December 24, 1909, deepened Twain's gloom. On May 20, 1909, his close friend Henry Rogers died suddenly.

In April 1906, Twain heard that his friend Ina Coolbrith had lost nearly all that she owned in the 1906 San Francisco earthquake, and he volunteered a few autographed portrait photographs to be sold for her benefit. To further aid Coolbrith, George Wharton James visited Twain in New York and arranged for a new portrait session. Twain was resistant initially, but he eventually admitted that four of the resulting images were the finest ones ever taken of him. In September, Twain started publishing chapters from his autobiography in the North American Review. The same year, Charlotte Teller, a writer living with her grandmother at 3 Fifth Avenue, began an acquaintanceship with him which "lasted several years and may have included romantic intentions" on his part.

In 1906, Twain formed the Angel Fish and Aquarium Club, for girls whom he viewed as surrogate granddaughters. Its dozen or so members ranged in age from 10 to 16. Twain exchanged letters with his "Angel Fish" girls and invited them to concerts and the theatre and to play games. Twain wrote in 1908 that the club was his "life's chief delight". In 1907, he met Dorothy Quick (then age 11) on a transatlantic crossing, beginning "a friendship that was to last until the very day of his death".

Twain was awarded an honorary Doctor of Letters (D.Litt.) by Yale University in 1901 and a Doctor of Law by the University of Missouri in 1902. Oxford University awarded him a Doctorate of Law in 1907.

Twain was born two weeks after Halley's Comet 's closest approach in 1835; he said in 1909:

I came in with Halley's Comet in 1835. It is coming again next year, and I expect to go out with it. It will be the greatest disappointment of my life if I don't go out with Halley's Comet. The Almighty has said, no doubt: "Now here are these two unaccountable freaks; they came in together, they must go out together".

Twain's prediction was eerily accurate; he died of a heart attack on April 21, 1910, in Stormfield, one month before the comet passed Earth that year.

Upon hearing of Twain's death, President William Howard Taft said:

Mark Twain gave pleasure – real intellectual enjoyment – to millions, and his works will continue to give such pleasure to millions yet to come … His humor was American, but he was nearly as much appreciated by Englishmen and people of other countries as by his own countrymen. He has made an enduring part of American literature.

Twain's funeral was at the Brick Presbyterian Church on Fifth Avenue, New York. He is buried in his wife's family plot at Woodlawn Cemetery in Elmira, New York. The Langdon family plot is marked by a 12-foot monument (two fathoms, or "mark twain") placed there by Twain's surviving daughter Clara. There is also a smaller headstone. He expressed a preference for cremation (for example, in Life on the Mississippi), but he acknowledged that his surviving family would have the last word.

Officials in Connecticut and New York estimated the value of Twain's estate at $471,000 ($ 11,000,000 in 2023).