This was a very tricky question, because it depends on interpretation!
These are the single-letter chapters I have as inactive:
Beta--Colby College
Chi (Old)--Jessamine Institute
Delta--Dickinson College
Epsilon (#1)--Barnard
Epsilon (#2)--SUNY-Buffalo
Phi (#1)--Hellmuth Woman's College
Phi (#2)--USC
Sigma--Randolph-Macon
Tau (Old)--Ole Miss (Oxford)
Upsilon (#1)--Belmont College
Upsilon (#2)--Southwestern Baptist/Union
According to that list, 11 chapters have closed. But if you count each letter once, only 8 chapters have closed (did I even list that as a choice?!) Plus I don't really understand why Ole Miss has two different listings as Tau...unless it was a community chapter versus a collegiate chapter? Nutbrnhair, you are our resident expert, any clarification?
PS--According to the 1920 edition of Baird's, Phi Chapter was the first to close, in 1899. This contradicts the other information we were given, so now I have no clue!!