I know there is an old, old thread about this, but I am not good at the search function.
AOII does not use any order. We allow our colonies to select their own designation. The designation must also then stand for the chapter sub-motto. My chapter at the University of Illinois wanted to use
Iota for
Illinois, so they chose the sub-motto
iso fore which is Greek for
sharing equal burdens. Some use an English sub-motto, for example
Alpha
Gamma's is "
always
genuine" and
Tau
Delta's is "
true to
duty."
Most of our oldest chapters are our single-lettered ones, but those are not in order, and actually some of our oldest 24 chose double-letter designations, and the single letter "Mu" was never used to name a chapter. So in order of founding, our oldest chapters are:
Alpha (Barnard/Columbia)
Pi (Sophie Newcomb/Tulane)
Nu (NYU)
Omicron (Tennessee)
Kappa (Randolph-Macon Women's College)
Zeta (Nebraska)
Sigma (Cal-Berkeley)
Theta (DePauw)
Beta (Brown)
Delta (Tufts)
Gamma (Maine)
Epsilon (Cornell)
Rho (Northwestern)
Lambda (Stanford)
Iota (Illinois)
Tau (Minnesota)
Chi (Syracuse)
Upsilon (Washington)
Nu Kappa (Southern Methodist)
Beta Phi (Indiana)
Eta (Wisonsin)
Alpha Phi (Montana State)
Nu Omicron (Vanderbilt)
Psi (Penn)
Phi (Kansas)
Omega (Miami Ohio)
Omicron Pi (Michigan)
Alpha Sigma (Oregon)
Xi (Oklahoma)