Uncle Sam is usually regarded as having made his home in Troy, New York (or at least that is what I always was taught while growing up in the Albany area) and had been a butcher who sent supplies to soldiers during the Civil War. From what I understand he got the nickname from the labels on the rations and it spread among troops though he didn't become the figure that he is now until the early 1900's when he became the more fictional Sam that we see now.

Source: Grew up in his "hometown" and learned about the history of Uncle Sam during school.