History

The oldest Greek letter organization is Phi Beta Kappa. It was created on Dec. 5, 1776 at William and Mary.
The number of Greek letter societies in the USA and overseas is large and not known. The list below contains the oldest and most influential in the US.

Phi Beta Kappa, 1776, William and Mary.
Kappa Alpha, 1825, Union.
Sigma Phi, 1827, Union.
Delta Phi, 1827, Union.
Alpha Delta Phi, 1832, Hamilton.
Psi Upsilon, 1833, Union.
Chi Psi, 1841, Union.
Delta Kappa Epsilon, 1844, Yale.
Delta Psi, 1847, Columbia.
Theta Delta Chi, 1847, Union.
Zeta Psi, 1847, N. Y. Uni.