Land records 1792-1886 for the District of Columbia are available through your local Family History Center, once they re-open.
Maryland land records are on-line at https://mdlandrec.net/main/index.cfm (you will need to sign up for a user name and password)
Thanks for the help. Great information.
Welcome to History Hub
The Rock of Dumbarton is in Georgetown, Kent County, Maryland
According to the list of Historic Places in Maryland it was owned by Colonel Ninian Beall not Thomas
Dumbarton is the Headquarters of The National Society of the Colonial Dames of America.
You should contact the Colonial Dames of America with your questions about the deed....https://nscda.org/
They are also on Facebook
Tour of the House https://dumbartonhouse.org/visit-dumbarton-house/virtual-tour/
Thank you for the help. I sent them an email.
I would have been stuck in the mud if it wasn't for history hub.
Dear Mr. Baxter,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located a series titled the National Register of Historic Places and National Historic Landmarks Program Records, 2013 - 2017 in the Records of the National Park Service (Record Group 79) that includes a file unit titled National Register of Historic Places and National Historic Landmarks Program Records: Washington, DC with a digitized item Washington, DC SP Dumbarton House which contains a reference to property ownership and subsequent transfers on page 12-13. The digitized item is available via the Catalog.
We also located the series Deedbooks, 1792 - 1869 in the Records of the Government of the District of Columbia (Record Group 351) that may include the deed that you seek. For access to this series, please contact the National Archives at Washington, DC - Textual Reference (RDT1) via email at email@example.com.
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request from RDT1. We apologize for this inconvenience and appreciate your understanding and patience.
In addition, we suggest that you contact the National Society of The Colonial Dames of America (NSCDA) - Dumbarton House for additional information about the surrounding property of Thomas Beall.
We hope this is helpful. Best of luck with your research!