Margaret Dunn
Margaret Dunn was born in New York about 1819. About 1851 she became the second wife of William John Haddock, an Irish-born tobacco merchant who ran a cigar business on West Street with his brother Arthur. William had four children by his first wife, Sarah Jane Moore, who died in January 1848.
In 1852 William built a brick house at No. 276 West 11th Street in Greenwich Village, and the family lived there. Margaret had two children who appear with her in the census, Arthur Henry, born about 1852, and Margaret Isabella, born on 7 June 1855. A family tree adds a son Nathaniel, born about 1858, who is not in the 1860 household.
In the summer of 1860 the census found the household in the Ninth Ward: William, 55, Margaret, 41, his brother Arthur H. M. Haddock, his four children by his first marriage, now aged 17 to 23, her son Arthur, 8, her daughter "Maggie," 5, and a servant, Mary Cunningham.
A Margaret Haddock was buried in the Haddock family lot at Green-Wood Cemetery in Brooklyn on 10 November 1860. She was very probably this Margaret, five months after the census, since William married his third wife, Jane Moody, in 1862, and by 1880 his wife was Jane. Her daughter Margaret Isabella was then five.
Her maiden name survives in the records of her daughter's life: Margaret Isabella's marriage to Dr. Joseph F. Terriberry at Brooklyn in 1887 and her death at Canaan, Connecticut, in 1946 both give her mother as Margaret Dunn. Her own parents are not known.
Sources
If Margaret Dunn is in your family, start your own tree.
Cite: Heirology, "Margaret Dunn (1819-1860)", https://heirology.com/ancestors/margaret-dunn-1819-1860-9f449b.