Thanks for bumping up this thread. I am from Indiana originally, and yes, there are several greek-lettered social/philanthropic groups for women there. Kind of like the Junior League for small midwestern towns. My mother was active in Tri Kappa, and I was initiated when I graduated from HS. I can assure you that it had N-O-T-H-I-N-G to do with the Ku Klux Klan! We had quilt raffles to raise money for scholarships, and I think the chapter in my town may have had a bridge club. Pretty benign!
At least in the town where I grew up, joining was not a huge issue. Either by rule or tradition (I'm not sure which) you only joined one. As one other poster pointed out, you were more likely to be pursued by several organizations once you moved to town. Some of the female teachers at my HS were in Psi-otes (Psi Iota Xi) and were "recruiting" a group of us senior girls, but since I was a Tri Kappa "legacy," I didn't get the hard sell.
I went to college out of state and then moved away, so I was only active for a very brief period of time, but I can tell you that the members of all of those groups in Indiana do very good work.
ETA: and we used to sell an awesome cookbook!