George’s son John had began clearing the island around 1800 and started to develop it into a functional plantation. The island that we today experience as a forested wilderness was at this point taken up with carefully laid out fields of crops. A large tree lined boulevard ran north-south down the center of the island and lead visitors to a handsome Georgian Revival style mansion around the current location of the highway overpass.

John had friends in Washington high society, and apparently he maintained a perpetual open house at the mansion, with its well stocked wine cellars and stately ballroom. Presidents Washington, Jefferson, Madison and Monroe; Chief Justice John Marshall, and King Louis of France (the one who got guillotined) are all known to have visited the island.

To the south of the mansion were formal gardens, and a smattering of smaller buildings including slave quarters, kitchens, workshops, and an ice house.

In 1831 the Mason family were forced to leave their mansion on the Potomac. Numerous histories of Theodore Roosevelt Island attribute this to the nuisance of stagnant water and bugs.

Unfortunately that isn’t the case. The definitively researched Historic American Landscape Survey records that “beginning in 1815 [John Mason] endured a series of poor investments and business ventures … unable to pay back his debts, the bank foreclosed on the island and 1,800 acres of Mason's land in northern Virginia, although it became polite convention among local residents to attribute his departure to the terrible mosquitoes.”