Q116. "I am wondering who actually was the first to sign the Constitution and when was it signed?"
A. The answer to the second question can be found quite easily by checking the Constitution itself. The answer to the first question is actually a little harder to determine. An image of the last page shows the signatures of the conventioneers, and though that of George Washington is at the top, that does not mean that he signed first. He signed his name as "President and deputy from Virginia," so maybe he signed when the others from Virginia signed. The signature of William Jackson, the secretary of the convention, is also prominent. That of George Read is first in the left hand column, and John Langdon is first in the right hand column. The point is, looking at the document is not the best way to determine who signed first.
The best secondary source of information would be the Minutes taken by James Madison. But Madison's notes on this day, on this particular issue, are scant: "The members then proceeded to sign the instrument."
The next best source would be other papers or letters written by anyone at the Convention. Unfortunately, I do not have access to great resources in this area. I would call on anyone with such access to let me know if my final conclusion is rendered incorrect by any such paper.
The last source of information is books about the Convention. There are many, of which I have a few. After consulting with them, some merely parrot Madison's words, some note that the delegates signed in order of state, and one notes that Washington signed first. The authors of these books that did not state one way or the other are all correct, and the one that states that Washington signed first is providing an opinion based on reasonable deduction.
Using some reasonable deductions of my own, I've concluded that Washington signed first. The fact that his signature is at the top of the lists of names is one particularly telling fact. The respect that the conventioneers had for Washington as both a person and as the president of the convention is another indication that he would have been asked or have been expected to sign first. It is reasonable, then, to say with as much certainty as possible, that George Washington signed the Constitution first.