Fielding Lewis Fielding Lewis ( July 7 , 1725 – December 7 , 1781 ) was a Colonel during the American Revolutionary War and the brother - in - law of George Washington . A successful merchant in Fredericksburg , VA , he had a plantation , which later became known as Kenmore . Notable for its Georgian mansion , it was designated as a National Historic Landmark in the twentieth century . Early life and education . Lewis was born at Warner Hall , a plantation in Gloucester County , Virginia , the son of John Lewis ( 1694 - 1754 ) , a merchant and planter , and Frances Fielding ( c1702 - 1731 ) . He was the third of seven children . His paternal uncle , Robert Lewis ( 1704 - 1765 ) , became the grandfather of Meriwether Lewis , who would explore the Louisiana Purchase . His father had a store in Fredericksburg . In 1749 John Lewis had a fine retail building constructed to display his wares and provide space for a selling floor and storage . The sandstone quoins , usually found only on larger mansions , were a sign of his aspirations . His son Fielding joined him in the business , taking it over in the 1750s . The originally one - and - a - half story building was expanded to two stories in the early 19th century . Despite competition and changing tastes , the handsome building operated successfully as a store for nearly 100 years , until 1820 , when it was finally adapted for residential use . Donated to the Historic Fredericksburg Foundation in 1996 , the building has been studied and stabilized for restoration . It is believed to be one of the oldest retail buildings in the United States . The Lewis Store was listed on the National Register of Historic Places in 2013 . Marriage and family . Lewis married Catharine Washington on October 18 , 1746 . She was his second cousin , the daughter of John Washington ( a first cousin to George Washington ) and Catharine Whiting . They had three children before Catharine died on February 19 , 1750 . A few months later , on May 7 , 1750 , Lewis married Betty Washington ( 1733 - 1797 ) , the sister of George Washington and another second cousin . She was 17 years old . They had 11 children together . Betty outlived Lewis by 16 years , dying in 1797 . Their son Lawrence Lewis later married Eleanor Parke Custis , George Washington ' s adopted daughter and step - granddaughter , tying the families closely together . Career . Lewis was established as a successful merchant before the American Revolutionary War . He was appointed as Commissary General of Munitions during the war , and commissioned at the rank of Colonel . He and his second wife Betty resided on a plantation ( later named Kenmore ) in Fredericksburg . Like others in the planter elite , they were supported by the labor of slaves . Betty ' s mother Mary Ball Washington frequently visited them and had a favorite spot she called her " meditation rock " . In 1769 , Fielding and Betty started construction of a large Georgian mansion on their property , which was completed in 1775 . It has some of the most refined colonial interior finishes of any surviving mansion . Named by later owners as Kenmore Plantation , it has been designated a National Historic Landmark and is listed on the National Register of Historic Places . Lewis died in Fredericksburg in 1781 at the end of the Revolutionary War . Before her death in 1789 , Mary Washington asked to be buried at her favorite spot at Kenmore , and her daughter Betty arranged for that . In 1833 a memorial was started at Mary Washington ' s gravesite , but never completed . Following the United States Centennial in 1889 , numerous historic and lineage societies were formed ; the Mary Washington Memorial Association held fundraising events and commissioned a memorial for her gravesite . It was dedicated in 1894 at Mary Washington ' s gravesite in a ceremony presided over by President Grover Cleveland of the United States .