The Colross property originally occupied the entire 1100 block of Oronoco Street; Alexandria merchant John Potts developed it as a plantation and began building the mansion in 1799–1800.

The Colross mansion is a two-story, brick, Georgian-style structure that features an architectural plan similar to that of Mount Vernon and Woodlawn, and it was originally flanked by two wings.

According to local tradition, two children in the Mason family died on the property and were interred in the estate's burial vault.

[1][7][8] John Potts, a prominent Alexandria merchant, developed the Colross property as a forced-labor cash-crop farm.

[14] Colross was then purchased by Thomson Francis Mason (1785–1838), a prominent jurist, lawyer, councilman, judge of the Criminal Court of the District of Columbia, and mayor of Alexandria between 1827 and 1830.

[14][17] Around the same time Mason acquired Colross, he built Huntley in Fairfax County, Virginia as a rural retreat and summer villa.

Willcox also remarked on the "hospitality and civility of the head of the house", Pen Mason's mother, Elizabeth "Betsey" Clapham Price (1802–1873).

[10][13] According to local tradition and to Alexandria resident Julian Taylor, at least two Union deserters were executed with their backs against the estate's high brick exterior wall.

[10][14][17] In addition, a "famous 'bounty jumper'" by the name of Downey was also shot and killed against the wall after being captured by his own soldiers.

[17][23][24] While there, the Smoots' daughter Betty wrote, "the grounds included a whole square block and were enclosed with an ancient brick wall ten feet in height".

[23] The parents of Cornell University professor and activist Alice Cook (1903–1998) lived at the then-dilapidated Colross with her father's superior from the Southern Railway.

She remarked that Colross "had no gaslights, and running water only in the kitchen", and that the house "stood in the midst of railroad tracks".

[9][10][13][24] Between 1929 and 1932, John Munn purchased the mansion, dismantled it, and shipped the structure brick-by-brick to Princeton, New Jersey, where it was restored.

[9][10][11] As of 2015[update], Colross houses the admission and advancement offices of Princeton Day School, and serves as a venue for the institution's events.

[26] In Alexandria, the mansion's remaining brick foundation was buried beneath a slab of reinforced concrete for over 50 years.

[9] Structures on the site have since included a large 50-truck garage, Andy's Car Wash, a Dominion Virginia Power substation, and the Hennage Creative Printers facility.

[12] The mansion's roof is covered by gray slate and is further embellished with three dormer windows facing from the home's front façade.

[24] The urn remained in its location throughout the American Civil War and was later acquired by the Association for the Preservation of Virginia Antiquities.

[24] The former Colross land tract on the 1100 block of Oronoco Street, which is bounded by North Fayette, Oronoco, Henry, and Pendleton streets,[9][10][11][29] was purchased in 2003 by Diamond Properties, a real estate development company with plans to build a mixed-use mid-rise luxury condominium project called Monarch Condominium.

[9][10] Diamond Properties paid R. Christopher Goodwin & Associates Inc., a cultural resource management firm, about $100,000 to explore the site for historical artifacts and to ensure all burial plots had been removed.

[9] Discoveries included an underground domed brick cistern that served as a water purification system and evidence that enslaved people lived in outbuildings on the Colross estate.

[10] According to the Alexandria Economic Development Partnership, the delay in construction caused 79 condominium buyers to abandon their purchases.

[31] Virginia Mason (1830–1919), another daughter of Thomson and Elizabeth married William Hathorn Stewart Davidge at Colross on February 1, 1853.

[33] According to local tradition, two small Mason children, William and Ann, were playing in the estate's yard when a storm arrived.