John Neilson (c.1770—1827) was an Irish immigrant to the United States who eventually settled in Virginia and became a prominent 19th-century master carpenter and joiner, as well as architect and builder.
From that point until 1808 Neilson would live and work as a joiner at Monticello, Jefferson's home in Albemarle County, Virginia.
It was at Monticello that Neilson began his long collaboration with fellow master joiner James Dinsmore, who was also an Irishman from Ulster.
Then from 1809–10, Neilson worked on the expansion of Montpelier, the home of the fourth President of the United States, James Madison, located in Orange County, Virginia.
From 1817 to 1820, Neilson worked at Bremo, the Fluvanna County, Virginia, plantation of John Hartwell Cocke.