Recently Thonas Tomasi mentioned that he saw Simon & Garfunkel perform during the Winter Carnival of 1967 in Johnson (VT) at the Johnson State College. Probably in February 1967, but so far no definitive confirmation has been found.
But, in an article of their upcoming show in Burlington (1967 March 12) it is mentioned.
Read here the (1967-03-08) St. Albans Daily Messenger article:
Someonean exact date for the Johnson State College show?
Paul Simon - 'Time it was...it was' 
They did play Johnson State College. My father was there during that time and told me about it.