Raspberry Plain dates back to the Colonial era when George Mason III died in 1735 and did not leave a will. His holdings went to his eldest son, George Mason of Gunston Hall, author of the Bill of Rights. George Mason III's widow, Mrs. Ann Thomson, did not want her other two children to feel slighted in their inheritance, so she saved enough money to make a land deal know as the "Wild Lands" purchase. Over time, she bought 10,000 acres in Loudoun County that extended north from Leesburg, up the current Route 15 corridor. This land was divided up between her daughter, Mary and her son Thomson. Thomson Mason later added to his holdings in Loudoun by purchasing the Raspberry Plain property from Loudoun's first sheriff, Aeneas Campbell in 1760.
Thomson Mason of Raspberry Plain was a Burgess in the Virginia Assembly and one of the first trustees of Leesburg. In 1771 he built the mansion at Raspberry Plain where he raised his four children. His first wife died in 1772 and Thomson remarried several years later and fathered two more sons by his wife Elizabeth Wallace. Raspberry Plain was deeded to his oldest son Stevens Thomson Mason, senator and father of two sons and three beautiful daughters, Mary, Emily and Catherine. The three Mason girls were frequently guests at the White House in Washington, DC and considered to be the "belles of the ball." There are reports of them sitting in the upstairs portico window at Raspberry Plain and watching their many suitors on prancing horses ride up the long drive. All three girls married well; Mary married Benjamin Howard, Governor of Missouri, Catherine married the honorable Thomas Barry and Emily married William McCarty.