| Jacob A. Cantor | |
| State: | New York |
| District: | 20th |
| Party: | Democratic |
| Term Start: | November 4, 1913 |
| Term End: | March 3, 1915 |
| Preceded: | Francis B. Harrison |
| Office2: | 3rd Borough President of Manhattan |
| Term Start2: | January 1, 1902 |
| Term End2: | December 31, 1903 |
| Predecessor2: | James J. Coogan |
| Successor2: | John F. Ahearn |
| Office3: | President pro tempore of the New York State Senate |
| Term Start3: | 1892 |
| Term End3: | 1893 |
| Predecessor3: | Jacob Sloat Fassett |
| Successor3: | Charles T. Saxton |
| Office4: | Member of the New York State Senate |
| Term Start4: | January 1, 1888 |
| Term End4: | December 31, 1898 |
| Constituency4: | 10th district (1888–1893) 14th district (1894–1895) 20th district (1896–1898) |
| Predecessor4: | William C. Traphagen |
| Successor4: | Thomas F. Donnelly |
| State Assembly5: | New York |
| District5: | 23rd |
| Term Start5: | January 1, 1885 |
| Term End5: | December 31, 1887 |
| Predecessor5: | Daniel M. Van Cott |
| Successor5: | Nicholas R. O'Connor |
| Birth Date: | 6 December 1854 |
| Birth Place: | New York City, US |
| Death Place: | New York City, US |
| Spouse: | Julia Lewenthal, Lydia Greenbaum |
| Children: | 3 |
| Occupation: | Lawyer |
| Education: | City College of New York |
Jacob Aaron Cantor (December 6, 1854 - July 2, 1921) was an American lawyer and politician from New York who served as a United States representative from 1913 to 1915.
Cantor was born at 19 Second Street in New York, the son of Henry Cantor and Hannah Cantor, both natives of London. He was a reporter for the New York World from 1872 to 1877. At the same time, he studied law at the City College of New York, graduated in 1875.
On November 2, 1891, his first wife Julia (Lewenthal) Cantor died. On September 25, 1897, he married Lydia Greenbaum, and they had three children: Margaret, Ruth and John.
Cantor was admitted to the bar and commenced practice in New York City.
He was a delegate to the 1884 Democratic National Convention. He was a member of the New York State Assembly (New York Co., 23rd D.) in 1885, 1886 and 1887. He was a member of the New York State Senate from 1888 to 1898, sitting in the 111th through 121st New York State Legislatures (all three 20th D.); and was President pro tempore from 1892 to 1893.
He was Borough President of Manhattan from 1902 to 1903, elected on the fusion ticket headed by Seth Low for Mayor of New York City, nominated by the anti-Tammany Hall Democrats, Republicans and the Citizens Union.
Cantor was elected as a Democrat to the 63rd United States Congress to fill the vacancy caused by the resignation of Francis Burton Harrison, and served from November 4, 1913, to March 3, 1915. He unsuccessfully contested the election of Isaac Siegel to the 64th United States Congress.
Afterwards he resumed the practice of law in New York City.
He was president of the New York City Department of Taxes and Assessments from 1918 until his death.
Cantor died at his home at 2345 Broadway, in Manhattan, and was buried at the Mt. Hope Cemetery in Hastings-on-Hudson, New York.