William Allen Dart (October 25, 1814 – March 8, 1890) was an American lawyer and politician from New York.

[1] He worked on his father's farm, attended St. Lawrence Academy and taught school.

[1] He was appointed Postmaster of Potsdam in 1845, and was District Attorney of St. Lawrence County from 1845 to 1847.

In April 1861, he was appointed by President Abraham Lincoln as United States Attorney for the Northern District of New York, and remained in office until 1866 when he was removed by President Andrew Johnson.

In 1869, he was appointed by President Ulysses S. Grant as U.S. Consul-General at Montreal, Quebec, Canada, and remained in office until 1878 when he resumed his law practice at Potsdam, in partnership with his son-in-law George Z. Erwin (1840–1894).