to add to what BSUPhiSig'92 posted. Phi Sigma Kappa merged with Phi Sigma Epsilon in 1985. Phi Sigma Epsilon was founded February 20, 1910 at Kansas State Normal College in Emporia, now Emporia State University. So, in a way we have 2 founders days. Although I'm sure most chapters only really celebrate March 15th.

Delta Delta Delta, November 27 (Thanksgiving Eve), 1888, Boston University

Kappa Sigma Fraternity was founded on
Friday December 10, 1869
at the University of Virginia