Mary was the fourth daughter and fourth child (of 10) of Nathaniel Mitchell (1728-1773) and his wife Abigail (Harris) Mitchell Conkling (1731-1822). Mary's mother Abigail was married and widowed twice. Mary's parents were both natives of New Jersey where Mary was born and raised. Mary was baptized in December of 1760 at the historic Saint John's Episcopal Church in Elizabeth, New Jersey, built in 1707, and still standing. This is the same church where her parents were married in 1752 and the same church where her mother was baptized in 1731 and where her maternal and paternal grandparents are all buried.

Mary married Jonathan Whitaker on September 16, 1779 in Morristown, New Jersey. The marriage produced 10 children, 8 living to adulthood. Mary's step-brother William Conkling married husband Jonathan's older sister Rebekka Whitaker. Also her step-sister Ruth Conkling married Jonathan's older brother Stephen Whitaker, another Revolutionary War Veteran. These families Whitaker-Harris-Mitchell-Conkling were very inter-connected, extremely patriotic, and active participants in the American War for Independence.

Husband Jonathan was a veteran of the Revolutionary War. He served alongside Mary's three youngest maternal uncles - George, Thomas, and John Harris. They remained close friends. Her youngest uncle John Harris named one of his sons after her husband Jonathan - Jonathan Whitaker Harris (1798-1872).

After the conclusion of the Revolutionary War, Jonathan Whitaker moved wife Mary and his family west first to Fayette County, Pennsylvania then on to Ohio by the early 1800's.

After being widowed Mary went to live with her son William Whitaker in Warren County, Ohio until he died, predeceasing her. Mary then went to Clermont County, Ohio with one of her granddaughters. She was just one month shy of age 90 when she died.