Beall's Levels and Rock of Dunbarton, part of his landholdings, were surveyed in 1752 as a possible site for George Town (now Georgetown). Maryland offered Beall two lots in the town, along with the "price of condemnation" (remuneration). Beall protested the proceedings, though ended up accepting two lots. Maryland paid a total of 280 pounds to acquire the land from Beall, along with land owned by George Gordon.
Beall died on October 15, 1807 and was originally buried in a burial site alongside their home on N Street (at 31st Street). Around 1870, he was moved to the Presbyterian Burying Ground in Georgetown.
- Balch 1899, p. 37.
- Ecker, Grace Dunlop (1933). A Portrait of Old Georgetown. Garrett & Massie, Inc. pp. 1–6.
- Balch, Thomas Willing (1897). "Notes and Queries". Pennsylvania Magazine (Historical Society of Pennsylvania) XXI: p. 507.
- Proctor, John Clagett (March 27, 1932). "Old Georgetown in History of District". The Sunday Star. p. 67.
- Balch, Thomas Willing (1899). The Brooke Family of Whitchurch, Hampshire, England; Together With an Account of Acting-Governor Robert Brooke of Maryland and Colonel Ninian Beall of Maryland and Some of Their Descendants. Philadelphia: Press of Allen, Lane & Scott.