While attending a costume ball at a Brittany coast resort in Dinard, France, the twenty-one year old Helena met William Angus Drogo Montagu, 9th Duke of Manchester, who was then twenty-three.
 He was the only son of the late 8th Duke of Manchester and his wife, the Cuban American heiress Consuelo Yznaga.
 On 14 November 1900, they married at Marylebone Church in London without her father or his mother present.
 Reportedly, the Duke's mother did not believe reports of the marriage and "envinced extreme displeasure at the idea of her son marrying Miss Zimmerman."
 In 1903, her father bought them Kylemore Castle in Connemara, Ireland.
 In addition, the Manchester's owned a house in London, a country estate known as Kimbolton Castle and Tandragee Castle in Northern Ireland.
In 1906, he was a Privy Councillor and from 1906 to 1907, he was a Captain of the Yeomen of the Guard.
From their marriage, she was the mother of four, including:
Lady Mary Alice Montagu (1901–1962), who married Fendall Littlepage Gregory of Cuernavaca in 1949.

Alexander Montagu, 10th Duke of Manchester (1902–1977), who married an Australian, Nell Vere Stead in 1927.
After her death in 1966, he married the American Elizabeth (née Fullerton) Coleman Crocker (1913–2007) in 1969.

Lord Edward Eugene Fernando Montagu (1906–1954), who married Norah Macfarlane Potter, a daughter of Albert Edward Potter, in 1929.
They divorced in 1937 and he remarried to Dorothy Vera Peters in 1937.
They divorced in 1947 and he married Martha Bowen the same year.
After her death in 1951, he married Baroness Cora Kellie in 1952.
His fifth marriage was to Roberta Herold Joughlin in 1953.

Lady Ellen Millicent Louise Montagu (1908–1948), who married Herman Martin Hofer, second son of John Jacob Hofer of Zurich, in 1936.
They divorced in 1944 and she married Maj.
John Norman Shairp, son of Col.
Alexander Shairp, in 1945.

The Duke's family, long prominent in British society and politics had little wealth left despite a $1,000,000 trust left for him by his mother (which she inherited from her brother, the banker Fernando Yznaga).
This was compounded by the Duke's profligate gambling and spending on other women.
In 1920, because of the Duke's gambling debts, they were forced to sell Kylemore Castle to Benedictine nuns who established a monastery on the grounds.
 Helena's father gave her a fixed allowance, and was careful to set up his will so the Duke received nothing.
 Her father died in Cincinnati in December 1914 leaving an estate valued at $10,000,000 in trust.
By 1918, sixty-six petitions of bankruptcy had been filed against the Duke in the English courts.

After rumors in 1908, and separation proceedings in 1915, 1921, and 1925 (when it was announced an estrangement had existed since 1914), they were eventually divorced in December 1931 after the Duke absconded to Cuba in November to apply for a divorce there.
 Her remarried almost immediately to another American, the former actress Kathleen Dawes of Connecticut.
The Duke died in Seaford, Sussex in February 1947.
While attending a costume ball at a Brittany coast resort in Dinard, France, the twenty-one year old Helena met William Angus Drogo Montagu, 9th Duke of Manchester, who was then twenty-three.  He was the only son of the late 8th Duke of Manchester and his wife, the Cuban American heiress Consuelo Yznaga.  On 14 November 1900, they married at Marylebone Church in London without her father or his mother present.  Reportedly, the Duke's mother did not believe reports of the marriage and "envinced extreme displeasure at the idea of her son marrying Miss Zimmerman."  In 1903, her father bought them Kylemore Castle in Connemara, Ireland.  In addition, the Manchester's owned a house in London, a country estate known as Kimbolton Castle and Tandragee Castle in Northern Ireland. In 1906, he was a Privy Councillor and from 1906 to 1907, he was a Captain of the Yeomen of the Guard. From their marriage, she was the mother of four, including:
Lady Mary Alice Montagu (1901–1962), who married Fendall Littlepage Gregory of Cuernavaca in 1949.
Alexander Montagu, 10th Duke of Manchester (1902–1977), who married an Australian, Nell Vere Stead in 1927. After her death in 1966, he married the American Elizabeth (née Fullerton) Coleman Crocker (1913–2007) in 1969.
Lord Edward Eugene Fernando Montagu (1906–1954), who married Norah Macfarlane Potter, a daughter of Albert Edward Potter, in 1929. They divorced in 1937 and he remarried to Dorothy Vera Peters in 1937. They divorced in 1947 and he married Martha Bowen the same year. After her death in 1951, he married Baroness Cora Kellie in 1952. His fifth marriage was to Roberta Herold Joughlin in 1953.
Lady Ellen Millicent Louise Montagu (1908–1948), who married Herman Martin Hofer, second son of John Jacob Hofer of Zurich, in 1936. They divorced in 1944 and she married Maj. John Norman Shairp, son of Col. Alexander Shairp, in 1945.
The Duke's family, long prominent in British society and politics had little wealth left despite a $1,000,000 trust left for him by his mother (which she inherited from her brother, the banker Fernando Yznaga). This was compounded by the Duke's profligate gambling and spending on other women. In 1920, because of the Duke's gambling debts, they were forced to sell Kylemore Castle to Benedictine nuns who established a monastery on the grounds.  Helena's father gave her a fixed allowance, and was careful to set up his will so the Duke received nothing.  Her father died in Cincinnati in December 1914 leaving an estate valued at $10,000,000 in trust. By 1918, sixty-six petitions of bankruptcy had been filed against the Duke in the English courts.
After rumors in 1908, and separation proceedings in 1915, 1921, and 1925 (when it was announced an estrangement had existed since 1914), they were eventually divorced in December 1931 after the Duke absconded to Cuba in November to apply for a divorce there.  Her remarried almost immediately to another American, the former actress Kathleen Dawes of Connecticut. The Duke died in Seaford, Sussex in February 1947.
Helena, Countess of Kintore