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John Neilson (d. 1827) was an Irish joiner who worked, along with James Dinsmore and many others, on Thomas Jefferson's Monticello. He worked for Jefferson from 1804 to 1809, when he went to work for James Madison on his Montpelier estate. Neilson later went on to assist in the construction of the University of Virginia; he worked on Pavilions IX and X, seven dormitories, the Rotunda, and the Anatomical Theater .
Primary Source References 
1806 October. (Instructions to Edmund Bacon). "Mr. Dinsmore is to be furnished with bread grain from the mill. The proportion of corn and wheat is left to his own discretion. He provides his own provisions, and for Mr. Nelson and Barry."
1808 August 11. (Richard Barry to Jefferson). "I hope you'll excuse the liberty I take in sending a letter to Mr. Nelson under cover of yours." 
1813 March 4. (Jefferson to Thomas Munro). "You will therefore I presume be glad of the offer of good workmen from every quarter. Two such propose to offer themselves from hence, James Dinsmore and John Nielson...Neilson I also got from Philadelphia in 1804. and he lived with me 4. years and I have found him also an honest sober, and excellent man. Both are house joiners of the first order. They have done the whole of that work in my house, to which I can affirm there is nothing superior in the U.S. After they had finished with me they worked 2. or 3. years for the President, to whom therefore they are well known...The most difficult job you have is the dome of the Representatives, and I doubt if there be any men more equal to it than these...I strongly recommend these men to you, and if you employ them I shall have the double gratification of having served men worthy of trust, and of putting a public trust into worthy hands..." 
1817 April 17. (Jefferson to James Dinsmore). "I suppose the superintendence of the buildings will rest chiefly on myself as most convenient. So far as it does I should wish to commit it to yourself and Mr. Nelson, and while little is called for this year which might disturb your present engagements, it will open a great field of future employment for you. Will you undertake it? If you will, be so good as to let me hear from you as soon as you can, and I would rather wish it to be before the 6th. of May. There is a person here who wishes to offer you two very fine boys, his sons, as apprentices; but on this nothing need be said until you determine to come. Tender my esteem to mr. Nelson & be assured of it respectfully yourself." 
1820 May 31. (Jefferson to John Neilson). "I inclose you my note for the money due you, settled as you desired. My reason for allowing compound interest in this case (the only one in which I ever did so) was explained in conversing. I have taken 2. years for payment, because the fall of produce, likely to be permanent, were I to wait for crops, would too much retard the payment of monies due from me, and which I am anxious to discharge." 
2. Please note that this list should not be considered comprehensive.