John Mason ( planter ) John Mason ( April 4 , 1766 – March 19 , 1849 ) was an early American merchant , banker , and planter . As a son of George Mason , a Founding Father of the United States , Mason was a scion of the prominent Mason political family . Early life and education . Mason was born on April 4 , 1766 at Mattawoman plantation , the estate of his maternal grandparents William Eilbeck and Sarah Edgar Eilbeck . He was eighth child and fifth - eldest son of George Mason IV and his wife Ann Eilbeck . Like his brothers , Mason was tutored at his father ' s estate , Gunston Hall , in Fairfax County , Virginia . His tutors were Scotsmen Mr . Davidson and Mr . Constable . After the American Revolutionary War , Mason , his brother Thomas , and a cousin , studied with Reverend Buchnan , rector of Aquia and Pohick churches , who resided on Passapatanzy Creek . Mason completed his formal education in mathematics with another Scotsman , Mr . Hunter , in Calvert County , Maryland . He was then apprenticed to a Quaker merchant William Hartshorne of the firm of Harper & Hartshorne in Alexandria , Virginia . Mason accompanied his father George Mason to the Philadelphia Convention , but returned to continue his apprenticeship with Hartshorne before the Convention ended . Mason remained with Hartshorne until Spring 1788 when he then entered into a partnership with merchants James and Joseph Fenwick of Maryland . Merchant and banking career . On June 22 , 1788 , Mason travelled to Bordeaux , France to conduct business for Fenwick & Mason firm there . Despite the onset of the French Revolution , Mason remained in France until 1791 and only then left due to his ill health . The Bordeaux branch of Fenwick & Mason continued to thrive , but was liquidate d in 1793 because of the encroaching threat of war in Europe . Declining prices of tobacco were also partly to blame for the firm ' s Bordeaux closure . By Spring 1792 , Mason had established a branch of Fenwick & Mason in Georgetown . As the firm expanded , it became involved in a variety of other lucrative ventures including bankinging , international commerce , the organization of foundries , and navigation and turnpike companies . Fenwick & Mason also became involved in the flour and wheat trade in addition to its tobacco operations . Mason also served on the board of directors of the Bank of Columbia and became its president in 1798 . Around this same time , Mason purchased large tracts of land in the Federal City . His involvement with government service was enhanced through his 1807 appointment as Superintendent of the Indian Trade . Mason held this position until 1816 . Mason also served as a brigadier general in the District of Columbia militia . He was appointed by President Thomas Jefferson to be the first Commander of the District of Columbia militia in 1802 . Through this role , Mason became commissioner general of prisoners during the War of 1812 . In 1817 , he became the president of the Potomac Company . His nephew Thomson Francis Mason was later chairman of the Alexandria Canal further downstream . Mason acquired Henry Foxall ' s Foxhall Cannon Foundry in Georgetown in 1815 . Mason continued to operate the foundry until his death in 1849 . For five years after Mason ' s death , the foundry remained part of the Mason estate with Mason ' s son Maynadier Mason as its superintendent . Marriage and children . Mason married Anna Maria Murray , daughter of James Murray and his wife Sarah Ennalls Maynadier , in Annapolis , Maryland on February 10 , 1796 . The couple had ten children : Residences . Following Mason ' s marriage to Anna Maria Murray in 1796 , he settled in Georgetown on property located at the corner of present - day 25th and L Streets and Pennsylvania Avenue , Northwest . Mason also built a summer residence on Analostan Island ( now Theodore Roosevelt Island ) on the Potomac River , which became the scene of many elegant social activities in the District of Columbia . Analostan Island had been acquired by George Mason in 1724 . Mason inherited the Island from his father upon his death in 1792 and owned it until 1833 . The island was famous for its gardens , which were designed and installed by English gardener David Hepburn . Mason continued the operation of the ferry which crossed the Potomac River from Georgetown to the Virginia . After suffering a series of financial setbacks , Mason was forced to give up Analostan Island , and in 1833 , the family moved to Clermont in the Cameron Run valley in Fairfax County , Virginia . Mason and his family had already vacated the island in 1831 when a causeway stagnated the water in the Potomac River . Later life . Mason died on March 19 , 1849 at age 82 . His body was interred after March 19 , 1849 at Christ Church Cemetery in Alexandria , Virginia .