She was born Henrietta Howland Robinson in 1834 in New Bedford, Massachusetts, the daughter of Edward Mott Robinson and Abby Robinson (née Howland), the richest whaling family in the city. Her family members were Quakers who owned a large whaling fleet and also profited from the China trade. She had a younger brother who died as an infant. At the age of two, Hetty was living with her grandfather, Gideon Howland. Because of his influence and that of her father, and possibly because her mother was constantly ill, she took to her father's side and was reading financial papers to him by the age of six. When she was 13, Hetty became the family bookkeeper. At the age of 16, she enrolled at the Eliza Wing School where she remained until the age of 19.
Abby Robinson died in 1860 leaving her daughter $8,000 (equivalent to $213,000 in 2016). Shortly after her mother's death, an aunt bequeathed Hetty $20,000 (equivalent to $533,000 in 2016). Edward Robinson died in 1865 leaving Hetty approximately $5 million (equivalent to $78,228,000 in 2016) which included a $4 million trust fund that drew annual earnings. She used the money to invest in Civil War war bonds.
Hetty's aunt Sylvia Ann Howland also died in 1865. After Hetty learned that Sylvia Howland had willed most of her $2 million estate (equivalent to $31,291,000 in 2016) to charity, Hetty challenged the will's validity in court by producing an earlier will which allegedly left the entire estate to Hetty, and included a clause invalidating any subsequent wills. The case, Robinson v. Mandell, which is notable as an early example of the forensic use of mathematics, was ultimately decided against Robinson after the court ruled that the clause invalidating future wills, and Sylvia's signature to it, were forgeries. After five years of legal battles, Hetty was awarded $600,000 (equivalent to $11,364,000 in 2016).
On July 11, 1867, at the age of 33, Robinson married Edward Henry Green, a member of a wealthy Vermont family. She made him renounce all rights to her money before the wedding. The couple moved to his home in Manhattan. When her cousins tried to have her indicted for forgery based on the Robinson v. Mandell decision, the couple moved overseas to London, where they lived in the Langham Hotel. Their two children, Edward Howland Robinson "Ned" Green and Harriet Sylvia Ann Howland Green Wilks (called Sylvia), were born in London: Ned on August 23, 1868 and Sylvia on January 7, 1871.
While Green's husband Edward pursued investments as a sort of "gentleman banker", Hetty Green began parlaying her inheritances into her own astonishing fortune. She formulated an investment strategy to which she stuck throughout her life: conservative investments, substantial cash reserves to back up any movement, and an exceedingly cool head amidst turmoil. During her time in London, most of her investment efforts focused on greenbacks, the notes printed by the U.S. government immediately after the Civil War. When more timid investors were wary of notes put forth by the still-recovering government, Hetty Green bought at full bore, claiming to have made US$1.25 million from her bond investments in one year alone. Her earnings on that front were to fund her great subsequent rail-bond purchases.
When the Green family returned to the United States, they settled in Edward's hometown of Bellows Falls, Vermont. Already something of an eccentric, Green began to quarrel, not only with her husband and in-laws, but also with the domestic servants and neighborhood shopkeepers. After the 1885 collapse of the financial house John J. Cisco & Son, in which Hetty Green was the largest investor, investigation revealed that Edward had been the firm's greatest debtor. The firm's management had surreptitiously used her wealth as the basis for their loans to Edward.
Emphasizing that their finances were separate, Green withdrew her securities and deposited them in Chemical Bank. Edward moved out of their home. In later years, they would effect at least a partial reconciliation. Hetty helped nurse Edward in the years before his death on March 19, 1902, from heart disease and chronic nephritis. He was buried in Bellows Falls in the graveyard of Immanuel Church.
Hetty Green's stinginess was legendary. She was said never to turn on the heat or use hot water. She wore one old black dress and undergarments that she changed only after they had been worn out, did not wash her hands and rode in an old carriage. She ate mostly pies that cost fifteen cents. One tale claims that Green spent half a night searching her carriage for a lost stamp worth two cents. Another asserts that she instructed her laundress to wash only the dirtiest parts of her dresses (the hems) to save money on soap.
Green conducted much of her business at the offices of the Seaboard National Bank in New York, surrounded by trunks and suitcases full of her papers; she did not want to pay rent for her own office. Later unfounded rumors claimed that she ate only oatmeal, heated on the office radiator. Possibly because of the stiff competition of the mostly male business environment and partly because of her usually dour dress (due mainly to frugality, but perhaps in part related to her Quaker upbringing), she was given the nickname "the Witch of Wall Street".
She was a successful businesswoman who dealt mainly in real estate, invested in railroads and mines, and lent money while acquiring numerous mortgages. The City of New York came to Green for loans to keep the city afloat on several occasions, most particularly during the Panic of 1907; she wrote a check for $1.1 million and took her payment in short-term revenue bonds. Keenly detail-oriented, she would travel thousands of miles alone—in an era when few women would dare travel unescorted—to collect a debt of a few hundred dollars.
Green entered the lexicon of turn-of-the-century America with the popular phrase "I'm not Hetty if I do look green." O. Henry used this phrase in his 1890s story The Skylight Room when a young woman, negotiating the rent on a room in a rooming house owned by an imperious old lady, wishes to make it clear she is neither as rich as she appears nor as naive.
Her frugality extended to family life. When her son Ned broke his leg as a child, Hetty tried to have him admitted to a free clinic for the poor. Mythic accounts have her storming away after being recognized; her biographer Slack says that she paid her bill and took her son to other doctors. His leg did not heal properly and, after years of treatment, it had to be amputated.
As a young man, Ned moved away from his mother to manage the family's properties in Chicago and, later, Texas. In middle age, he returned to New York; his mother lived her final months with him.
Green's daughter Sylvia lived with her mother until her thirties. Hetty Green disapproved of all of her daughter's suitors, suspecting that they were after her fortune. Sylvia finally married Matthew Astor Wilks on February 23, 1909, after a two-year courtship. A minor heir to the Astor fortune, Wilks entered the marriage with $2 million of his own, enough to assure Green that he was not a gold digger. Nonetheless, she compelled him to sign a prenuptial agreement waiving his right to inherit Sylvia's fortune.
When her grown children left home, Green moved repeatedly among small apartments in Brooklyn Heights and Hoboken, New Jersey, mainly to avoid establishing a residence permanent enough to attract the attention of tax officials in any state. In her old age, she developed a bad hernia, but refused to have an operation because it cost $150. She suffered many strokes and had to rely on a wheelchair. She also became afraid that she would be kidnapped and made detours to evade would-be pursuers. She began to suspect that her aunt and father had been poisoned.
On July 3, 1916, Hetty Green died at age 81 at her son's New York City home. According to her longstanding "World's Greatest Miser" entry in the Guinness Book of World Records, she died of apoplexy after arguing with a maid over the virtues of skimmed milk. The New York Times reported she suffered a series of strokes leading up to her death.
Estimates of her net worth ranged from $100 million to $200 million (equivalent to $2.2 billion to $4.4 billion in 2017), making her arguably the richest woman in the world at the time. She was buried in Bellows Falls, Vermont, next to her husband. She had converted late in life to his Episcopalian faith so that she could be interred with him.
Their two children split her estate. They were reported to have enjoyed their wealth more than she had. Both notably came through the Great Depression relatively unscathed by following Hetty's philosophy of conservative buying backed by substantial cash reserves. Ned was an accomplished collector with interests in everything from auto racing to science to horticulture. After his death, his sister Sylvia, as heir, donated his Round Hill, Massachusetts estate in 1948 to the Massachusetts Institute of Technology (MIT), which used the property for certain experiments. These included a prototype atom smasher. They used his powerful WMAF radio transmitters to keep in touch with Richard E. Byrd's 1928-30 Antarctic expedition.
Sylvia died in 1951, leaving an estimated $200 million and donating all but $1,388,000 to 64 colleges, churches, hospitals, and other charities. Both children were buried near their parents in Bellows Falls.