I'm bored at work and found this.
Sigma Nu's oldest continuing would be Beta at U. of Virginia (1871). Alpha was at VMI.
As a side note, I visited Kansas chapter (Nu 1884) back when I was in college. I was soooooo blown away when I walked into the formal dining area and the walls were all lined with Composites going back to the 1800's. Just wow..... (Hope they get their charter back soon
)